Wetwood in Trees: Forest Service Pacific Northwest a Timber Resource Forest and Range Experiment Station General Technical Problem Report PNW- 112 EDITOR's J.C

United States Department of Agriculture Wetwood in Trees: Forest Service Pacific Northwest A Timber Resource Forest and Range Experiment Station General Technical Problem Report PNW- 112 EDITOR'S J.C. Ward and W.Y. Pong August 1980 FILE COPY

This file was created by scanning the printed publication. Mis-scans identified by the software have been corrected; however, some errors may remain. Abstract Contents

Available information on wetwood is pre- Page sented. Wetwood is a type of heartwood which has been internally infused with INTRODUCTION...... 1 water. Wetwood is responsible for substantial losses of wood, energy and CHARACTERISTICS OF WETWOOD...... 1 production expenditures in the forest products industry. CAUSES OF WETWOOD FORMATION ...... 2

The need to evaluate these losses and to WETWOOD IN TREES AND LOGS ...... 4 find ways to eliminate or minimize them is Occurrence...... 4 emphasized. Types of Wetwood and Patterns Within the Tree...... 8 Because of increased interest in wetwood, excellent opportunities exist in initiating WElWOOD PROPERTIES--A MICROBIAL a comprehensive program of research. Both IMPLICATION ...... 10 short and long-term studies are included in Odor...... 10 the program with the short-term studies Hydrogen Ion Concentration or pH. .. 10 answering the immediate utilization prob- Anaerobiosis...... 12 lems created by wetwood and the long-term Strength Properties ...... 12 studies directed at examining the causes of Permeability...... 14 wetwood and its control and prevention. ' Chemical Brown Stain Precursors ... 15

TIMBER UTILIZATION AND WOOD PROCESSING PROBLEMS ...... 16 Shake and Frost Cracks...... 16 Checking and Collapse ...... 19 Slow Drying Rates and Uneven Metric Equivalents Moisture Content ...... 23 Chemical Brown Stain...... 28 1 inch = 2.54 centimeters J Plywood and Reconstituted Boards. .. 32 1 foot = 0.304 8 meter Corrosion of Kilns...... 33 1 cubic foot = 0.028 32 cubic meter 1 pound = 0.453' 6 kilogram RESEARCHNEEDS...... 34 1 pound/square inch = 0.070 38 kilogram/ Short Term ...... 34 square centimeter LongTerm...... 38 5/9 (OF-32) = OC CONCLUSION...... 41 LITERATURE CITED...... 41

3. C Ward is row-irch forest products technologis:, TJ S Fore:! ?i-cdu.c:ts Laboratory, Madxon, 'bVisconsin. w M. bnq 1s research forest products tcch.;ar;rlogiai, Paczfic Northwest Forest az,d Esnge Exgerirrient Station, Portland, Oregon. Introduction Characteristics of Wetwood

This paper summarizes available information on the timber quality characteristic described as wetwood. Included are some possible causes of wetwood, where it occurs in trees, its properties, and the problems associated with it. The need for research to solve utilization problems associated with wetwood and the processing of logs and products containing it is recognized.

With this report as a guide, a concerted Wetwood is a type of heartwood in standing research effort directed at the problem of trees which has been internally infused wetwood can be organized. Such research with water (64, 2, 142). Wood infused will, in the short run, target in on and with water from an external source (e.g*, provide answers to wetwood-related proc- logs exposed to spray, rain, or storage essing problems presently plaguing industry ponds) does not fit this definition. In and, at the same time, build a base of sci- some tree species, wetwood often has a entific knowledge with which to solve the water-soaked translucent appearance and is problem of wetwood in timber stands. variously designated as water core, sinker heart, wet core, wet heart, and discolored wood. When frozen, the water-soaked wetwood appears as a distinct, hard, glossy surface on the ends of winter-cut logs of Scots pine (Pinus sylvestris 4.) (117) and balsam fir (164)- .&/ In other species, the typical water-soaked appearance may be absent. In this case, wetwood has the appearance of either normal heartwood or it has an unusually dark color. This dark color leads to the term 'I fa Is e " or ''pa tholog ica 1'I hea r twood . Red heart in white or paper birch is a type of wetwood/(z, 68). One type of wetwood in white fir is called blackheart (146).

LlScientif ic names of commercial North American tree species mentioned in this report are listed in table 1 (conifers), page 5, and table 2 (hardwoods) I page 6. ?/R. W. Davidson, Colorado State Univer- sity, personal communication to J. C. Ward.

1 Causes of Wetwood Formation

In general, wetwood is higher in moisture Wetwood in trees has been attributed to a content than the adjacent normal heart- number of causes: microbial wood. Reports of unusually high moisture (bacterial) , nonmicrobial (injury), and content in heartwood may result from an normal age-growth formation. Associative investigator's inability to recognize relationships have been the basis of many wetwood. In comparison with sapwood, evaluations of the causes of wetwood; wetwood can be higher in moisture content actual tests to confirm cause-and-effect (67,--- 79, 106, -117, -197) or lower or equal relationships have had little success. in moisture (20, 48, 121, 133, 203, 212, 215) . Regardless of external appearance, huch of the research on wetwood has wetwood differs from normal wood in been directed toward investigating the physical and chemical properties and association of bacterial infection and the generally is more difficult to dry, occurrence of wetwood in trees (20, 2, 46, -49, 60, 78, 2, 93, 106, 158, 167, 168, 190, 191, 202, 203, 206, 207, 214, 217, 219). Not all of these studies have found bacteria to be associated with wetwood. Bacteria have frequently been isolated from healthy sapwood and heartwood of living trees (12,13, 40, 107, 144, 190, 3).

The concept that wetwood is the result of a mixed population or invasion of more than one species of bacteria could explain some of the differences in results. This concept would be analogous to the successions of organisms in the development of wood decay and associated discol~orations described by Shigo (171) and Shigo and Hillis (173). Strictly anaerobic bacteria as well as facultative anaerobes have been isolated from wetwood (158, 174, 199, 202, -203, 205, 206, 222). Laboratory techniques for isolating and culturing strictly anaerobic bacteria are different from those for aerobic and facultative anaerobes and fungi. This could explain why investiga- tive results do not always agree about the relative importance of bacteria to formation of wetwood.

That wetwood formation or initiation may be nonmicrobial in nature has been suggested 'by some investigators (20, 45, 107, 144) and implied by others (12,40, 190). These investigations conclude that bacteria are part of an indigenous microflora of normal wood, living in a viable but quiescent state until some change occurs in the wood to provide a favorable substrate (wetwood) for the bacterial growth. Bacteria iso-

2 lated from wetwood of poplar utilized toe in true firs/(216) . A fairly con- capillary liquid from sapwood and heartwood sistent association between wetwood and for growth (190). decay has been,noted in eastern Oregon true firs/ and other tree species (2). We have observed that internal heart rot in tree stems often has a peripheral ring of sound wetwood, whereas stems with wetwood do not necessarily have associated decay. There is some belief that wetwood may inhibit decay (93).

The inability to consistently associate wetwood with micro-organisms has led to the conclusion that wetwood in conifers is only a condition of excessive accumulation of Wetwooa has been associated with physical, moisture and not a symptom of disease mechanical, and biological injurie&/(20 , (142,- 165) . There are opposing views on the -79, 186). Whether these injuries result in source of the excessive moisture in wetwood formation or initiate it has not wetwood. Some suggest direct entry of been substantiated. Field observations atmospheric moisture through stem openings, have shown that the normal cylindrical form such as dead branch stubs (20);others of wetwood in white fir deviated radially believe water in wetwood has an internal origin from moisture sources in the root and longitudinally to regions of natural * and silvicultural injuries (observations by and stem (9,3). In Japan the Occurrence W. Y. Pong). Similar deviations have been of wet heartwood is considered normal for noted in conjunction with injuries some species of hardwoods and abnormal for apparently caused by insect attack&/(=, conifers (220). Whether formation of -79, 211) and stem cankers of dwarf mistle- wetwood is the result of a natural process of the tree or is bacterial in origin is discussed at length by Hartley, et al. Until additional evidence is ~~~ ~ (E). ?/W. Y. Pong. 1967. Preliminary study of available, we will consider wetwood the grade defects in true firs. 1nterim.rep. manifestation of a syndrome of abnormal USDA For. Serv. Pac. Southwest For. and physiological events in the living tree and Range Exp. Stn., 31 p. Berkeley, Calif. not a specific disease. (Unpublished report on file at Pac. Northwest For. and Range Exp. Stn., 51 J. R. Parmeter, Department of Plant Port land, Oreg ) . Pathology, University of California, 4/ Personal communication to W. Y. POW Berkeley, personal communication to W. Y. from K. R. Shea, Assistant Director, Pong. Science and Education Administration, U.S. /Field observations by P. E. Aho, Department of Agriculture, Washington D.C., Forestry Sciences Laboratory, Corvallis, and from W. W. Wilcox, Forest Products Oreg . Laboratory, University of California, Richmond .

3 Wetwood in Trees and hogs oc cur nc e

Wetwood occurs in both conifers and hardwoods, but its frequency can vary by species, age, and growing conditions of trees. Occurrence of wetwood in the more important commercial timber species of North America is presented in table 1 for softwoods and table 2 for hardwoods. Each species is listed by its apparent suscepti- Not all the tree species in class 3 are bility to wetwood formation. These affected with wetwood to the same degree or classifications are derived from our obser- frequency. There are differences within a vations, personal communications from genus: for example, white fir and grand f ir colleagues, office reports, and the are affected more than are noble fir and published literature. Tree species in Pacific silver fir. From his studies with which wetwood either has never been white fir in northern California, reported or is rarely observed are placed Wilcod/ found that all sample trees, in class 1. Class 3 includes the most including young ones, contained some susceptible tree species or those that can wetwood. This appears to be the rule for be expected to develop wetwood either with white fir in northern California, but in age or under less than optimum growing some stands wetwood appears to be rare or conditions. The intermediate class 2 nonexistent .8/ The presence of wetwood contains species in which wetwood is found within the hardwood genus Populus appears in one locality and rarely, if at all, in to be the rule, but again there can be another reg ion. exceptions. Some investigators could not find eastern cottonwood trees that were free ot wetwoo&/ (191, 222) . For For some species in both tables 1 and 2, Earopean white poplar (Populus alba L.), the information is tentative; as additional the presence of wetwood is the rule in field information becomes available a pistillate trees and the exception in species may be moved from one class to staminate treesl0/(z) another. Sufficient information exists to indicate that wetwood will probably develop in hemlocks, true firs, and cottonwoods W. W. Wilcox, Forest Products from most regions. For species such as Laboratory, University of California, white pine, red oak, and maple, wetwood is Richmond, personal communication to W. Y. found in many trees of one region and Pong. completely lacking in trees of another EIJ. C. Ward, unpublished data on file at region. Thus, if the rating of a species U.S. Forest Products Laboratory, Madison, in tables 1 and 2 is based on reports from Wis. a limited area of the total range of the 9/J. B. Baker, Southern Forest Experiment species, then its status could be reversed Station, New Orleans, La., personal when additional information is available. communication to J. C. Ward. e/J. C. Ward and J. G. Zeikus, unpublished data on file at U.S. Forest Products Laboratory, Madison, Wis.

4 Table 1--Occurrence of wetwood in'commercially important conifers of the United Stated'

Frequency ClaSS2/

Species 1 2 3 Occasional Scattered Generally or none prevalence prevalent

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco + Eastern hemlock (Tsuga canadensis (L.) Carr.) + Western hemlock (Tsuga heterophylla (Raf.) Sarg.) +' Mountain hemlock (Tsuga mertensiana (Bong.) Carr. -t- True fir: Balsam fir (Abies balsamea (L.) Mill.) +, White fir (Abies concolor (Gord. & Glend.) Lind11. ex Hildebr.) + Grand fir (Abies randis (Dougl.) ex D. Don) Lindl . ) +' Subalpine f-iocarpa (Hook. ) Nutt .) + Pacific silver fir (Abies amabilis (Dougl.) ex Forbes) Noble fir (Abies procera Rehd.) California red fir (Abies magnifica A. Murr.) Shasta red fir (Abies magnifica var. shastensis Lemm.) Spruce: White spruce (Picea glauca (Moench) Voss) + Black spruce (Picea mariana (Mill.) B.S.P.) + Red spruce (Picea rubens Sarg.) + Engelmann spruce (Picea engelmannii Parry ex Engelm.) + Sitka spruce (Picea sitchensis (Bong. ) Carr. ) + Soft pine: Eastern white pine (Pinus strobus L.) +' Western white pine (Pinus monticola Dougl. ex 0. Don) + Sugar pine (Pinus lambertiana Dougl.) + Hard pine: Jack pine (Pinus banksiana Lamb. ) + LodqepoleLodgepole pine (Pinus contorta Douql.Dougl. ex Loud.) + Red Dine (Pinus resinosa Ait.) + Ponderosa 'pine (Pinus ponderosa Dougl . ex Laws. ) + Shortleaf pine (Pinus echinata Mill.) + Lobloll9 pine (Pinus taeda L.) + Longleaf pine (Pinus palustris Mill.) + Slash pine (Pinus elliottii Engelm. var. elliottii) + Jeffrey pine (Pinus jeffreyi Grev. & Balf. + Western larch (Larix occidentalis Nutt.) + Tamarack (Larix laricina (Du Roiy K. Koch) + Redwood (Sequoia sempervirens (D. Don) Endl.) + Giant sequoia (Sequoia dendron giganteum (Lindl. ) Buchholz) + Baldcypress (Taxodium distichum (L.) Rich.) +' Cedar : Incense-cedar (LibocedriJS decurrens Torr.) + Western redcedar (Thu'a 1icata Donn ex 0. Do t Northern white-ced-identalis L. ) + Alaska-cedar (Chamaecyparis nootkatensis (D. Spach) :+ Port-Orford-cedar (Chamaecyparis lawsoniana ( Jrr.) Plarl. ) + Atlantic white-cedar (Chamaecyparis thyoides B.S.P. 1 + Eastern redcedar (Juniperus vi'rginiana L. ) + Juniper: Alligator juniper (Juniperus- deppeana Steud.) + Western juniper (Junipe:rus occidentalis Hook. +

1/From field observations by authors augmented with personal communications; also from literature, particularly Hartley et al. (79)- and Lutz (126). il/Frequency class 1 includes tree species in which wetNood rarely, if ever, occurs and species in which wetwood has not been observed, reported, or recognized as wetwood. Class 2 includes species in which wetwood will develop on some sites and not on other sites, together with species that tend to develop wetwood with increasing age on certain sites. Class 3 includes species very susceptible to formation of wetwood on most sites and in young- as well as old-growth timber.

5 Table Z--Occurrence of wetwood in commercially important hardwoods of the United Statesi/

Frequency classl/

Species 1 2 3 Occasional Scattered Generally or none prevalence prevalent

Red oak group: Northern red oak (Quercus rubra L.) Black oak (Quercus velutina Lam.) Scarlet oak (Quercus coccinea Muenchh.) Pin oak (Quercus palustris Muenchh.) Water oak (Quercus ni ra L.) Nutt a 11 oa k-t a1 1 i i Pa lme r ) + Southern red oak (Quercus falcata Michx. var. falcata) + Cherrybark oak (Quercus falcata Tar. pagodaefolia Ell. ) Willow oak (Quercus phellos L.) + Laurel oak (Quercus laurifolia Michx.) Shumard oak (Quercus shumardii Buckl. var. shumardii) + California black oak (Quercus kelloggii Newb.) White oak group: White oak (Quercus alba I-.) + Bur oak (Quercus macrocarpa Michx.) + Overcup oak (Quercus 1 rata Walt.) + Swamp white o-color Willd. ) + Chestnut oak (Quercus rhus L. + Swamp chestnut-*miciauxii Nutt . ) + Chinkapin oak (Quercus muehlenbergii Engelm. 1 + Post oak (Quercus stellata Wangenh. var. stellata Oregon white oak (Quercus garryana Dougl. ex Hook California white oak (Quercus lobata Nee) Tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehd Hickory : Bitternut hickory (Carya cordiformis (Wangenh. ) K. Koch) + Water hickory (Car a aquatica (Michx. f.) Nutt .> + Pecan (Carya illinoensis+ Wangenh. ) K. Koch) + Shagbark hickory (Car a ovata (Mill.) K. Koch) + Shellbark hickory bniosa(Michx. f. ) Loud. ) + Mockernut hickory (Car a tomentosa (Poir.) Nutt. 1 + Pignut hickory (Car-.) Sweet) + Black walnut (Juglans nigra L.) + Butternut (Juglans cinerea L.) + Sweetgum (Liquidambar styraciflua L.) + Maple: Sugar maple (Acer saccharum Marsh.) + Silver maple (Acer saccharinum L.) + Red maple (Acer rubrum L.) + Black maDle (Acer niarum Michx. f.) + Bigleaf maple-ophyllum Pursh 1 + Black tupelo (Nyssa sylvatica Marsh.) + + L.) + Magnolias’ (Magnolia L. spp. ) +

6 Table 2--Continued

~~~ ~

Frequency class?/

Species 1 2 3 Occasional Scattered Generally or none prevalence prevalent

Ash: White ash (Fraxinus americana L.) Green ash (Fraxinus pennsylvanica Marsh.) Black ash (Fraxinus ni ra Marsh. Oregon ash moli?Bknth.) American beech (Fagus grandifolia Ehrh.) Poplar and aspen: Eastern cottonwood (Populus deltoides Bartr. ex Ma rsh.) Plains cottonwood (Populus sargentii Dode4 Narrowleaf cottonwood (Powlus anaustifol.ia James) Black cottonwood (Populus' trichocirpa Torr. & Gray 1 Fremont cottonwood (Populus fremontii Wats.) Swamp cottonwood (Populus heterophylla L.) Balsam poplar (Populus balsamifera L.) Quaking aspen (Populus tremuloides Michx.) + Largetooth aspen (Populus grandidentata Michx .I + Black willow (Salix nigra Marsh.) + Red alder (Alnus rubra Bong.) + Birch: Paper birch (Betula papyrifera Marsh.) Gray birch (Betula populifolia Marsh.) Yellow birch (Betula alleghaniensis Britton) River birch (Betula ni ra L. American sycamodocLidentalis L .) + Black cherry (Prunus serotina Ehrh.) + Northern catalpa (Catalpa speciosa Warder ex Enlgelm. + Elm : American elm (Ulmus americana L.) + Slippery elm (Ulmus rubra MUhl.1 + Rock elm (Ulmus thomasii Sarg.)' Hackberry (Celtis occidentalis L.) Sugarberry XCeltis laevigata Willd.) Ohio buckeye (Aesculus labra Willd.) Yellow buckeye7--9-- Aesculus octandra Marsh. American basswood (Tilia americana L.) + White basswood (Tilia heterophylla Vent. + Pacific madrone (Arbutus menziesii Pursh + Red mulberry (Morus rubra L.) + Black locust (Robinia pseudoacacia L.) + Honey locust (Gleditsia triacanthos L. ) + Water locust (Gleditsia aquatica Marsh.) + Kentucky coffeetree (Gymnocladus dioicus (L.) K. Koch) +

~~~ ~~~ L/From field observations by authors augmented with personal commukcations; also from literature, particularly Hartley et al. (79)- and Lutz (126). !/Frequency class 1 includes 'tree species in wnich wetwood rarely, if ever, occurs and species in which wetwood has not been observed, reported, or recognized as wetwood. Class 2 includes species in which wetwood will develop on some sites and not on other sites, together with species that tend to develop wetwood with increasing age on certain sites. Class 3 includes species very susceptible to formation of wetwood on most sites and in young- as well as old-growth timber.

7 Even though considerable data may show that planting of scions in moist soil (see a species in class 1 is not susceptible to footnote 9). Second-growth aspen in wetwood formation, it may be important to northern Minnesota contains more wetwood continue looking for exceptions. For than aspen from the original forest.g/ example, we have rarely found wetwood in This may be due to the origin of the Douglas-fir and then it was limited in second-growth trees from sprouts and a volume to small streaks or pockets. different species composition of the Nevertheless, one small stand of second-growth stands favoring attacks by Douglas-fir timber in the Cascade Range of both micro-organisms and stem-boring Oregon contained extensive wetwood in the insects. Eis (53) found that root grafts logs, and the lumber was difficult to dry in natural stands of Douglas-fir, western to a uniform moisture c0ntent.W In hemlock, and western redcedar can be a Washington, a Douglas-f ir bridge timber major factor in the spread of decay organ- which failed from ring shake was found to isms from stumps to neighboring trees. have contained extensive bacterial wetwood Root grafts may also be a factor in the (see footnote 8). initiation and spread of wetwood. Cole and Streams (42)suggest that wetwood bacteria Age has some influence on formation of are spread by slime-flux insects. wetwood. In general, there is less wetwood in young trees: some foresters think that the problem will be solved when the last Types of Wetwood and old-growth timber is cut. In some species, such as cottonwood, aspen, elm, maple, and Patterns Within the Tree white fir, wetwood has been recorded in very young trees (see footnote 7) (E). With few exceptions, forriration of wetwood has been restricted to the heartwood and When wetwood is prevalent in young trees, heartwood-sapwood transition zones of site or cultural practices may be the major living trees. Essentially two types of contributing factors. Field observations wetwood can occur in the living tree: by the senior author indicate that site wetwood formeu from the aging of normal conditions may influence the incidence of sapwood nearest the heartwood or injured wetwood in young-growth western hemlock. sapwood and wetwood developed in previously Wallin (197) observed a relation between formed heartwood. The two types frequently wetwood formation in balsam poplar and soil occur together and are difficult to type. Wetwood is most prevalent in the d ist ing u ish. lower stems of western redcedar growing on wet, swampy sites (73,e). These soil or site factors may favor increases in populations of micro-organisms associated with wetwood. Similarly, cultural practices could contribute to the establishment and growth of these micro-organisms in trees. Most cottonwood trees grown in plantations on good soils in the Mississippi delta develop wetwood within 2 years. This is apparently related to the g/C. J. Kozlik, Department of Forest Products, Oregon State University, G/E. M. Ballman, Chief Forester, Diamond Corvallis, personal communication to J. C. International Corp., Cloquet, Minn., Ward. personal communication to J. C. Ward.

8 Although the spatial distribution of wetwood in standing trees will vary by point of origin, duration of formation, and other such factors, there are essentially three general patterns. Most common is the conical pattern in the ccntral core of the lower bole--the wetwood originates at injuries in the roots or at the root collar and tapers to an apex in the upper bole. This pattern has been found in true firs (45, 92, _147, 215) , western hemlock (203)- , Wetwood is generally not found in the outer northern red oak (B,z), eastern sapwood of living trees; reports to the cottonwood (see footnote 9), and western contrary indicate that such occurrence is larch (see footnote 8) . associated. with insect attack, stem cankers, and wounds of various forms (79, -91; also see footnotes 3, 5, and 7). In these instances, the wetwood zone of the central core deviated radially and long i- tudinally to the traumatized zone of the sapwood. Knutson (106), however, was not always able to relate wetwood in the sapwood of aspen to visible wounds, but he considered wetwood to be generally a phenomenon of the sapwood. Takizawa et al. (186) found from the cytology of wetwood in the Japanese fir Todomatsu (Abies The second pattern consists of streaks or sachalinensis Mast.) that wetwood was more columns of wetwood which can be traced to comparable to sapwood than heartwood but it injuries or to stubs of dead branches in existed as streaks in the outer heartwood. the upper stem. The basal portion of these trees may be free of wetwood. Upper stem wetwood has been noted in trembling aspen It is important that a distinction is made (106), cricket-bat willow (Salix alba var. between the wetwood or "sinker" stock calva G. F. W. Mey.) elm (i.e., wood that will not float) formed in (e), (z), eastern white pine silver fir (Abies the standing tree and the "sinker wetwood" (123), alba Mill) California white fir,r resulting from storage of logs in water. (20), and eastern and western hemlocel In pond-stored logs, the affected wood is (see footnote 11) mainly the sapwood and the wood of the . central core exposed on the log ends. Pond-stored logs cease to float because of increased permeability from bacterial G/A. L. Shigo, Forestry Sciences disintegration of pit membranes in the Laboratory, Durham, N. H. I personal sapwood but not the heartwood (44, 50, 55, communication to J. C. Ward. -69, 72, 90, 95, 105, 119, 157, 180, 195, -14/ Field observations by the authors. -208). In comparison, wetwood in standing trees is confined more to the heartwood and has registered lower permeability than the adjacent normal wood, particularly sapwood. The permeability of wetwood from trees is discussed in the section on properties of wetwood.

9 Wetwood Properties-- A Microbial Implication

The third pattern appears when a tree Wetwood has distinctive physical and chemi- contains both basal and upper stem wetwood cal properties. These properties appear formations that extend and coalesce into a to result from microbial action on woody single massive formation. This pattern was tissue in the living tree, but more noted in Scots pine and Norway spruce comprehensive tests are needed to validate (Picea abies (L.) Karst) by Lagerberg (117) this relationship. who also was the first to describe the other patterns. It is not uhcommon for aspen in Minnesota and Wisconsin (see Odor footnote 8) and balsam fir (E)to have the combined wetwood pattern. The odor of wetwood in the green condition differs from that of normal wood and is reminiscent of fermentation processes. This indicates an influence by anaerobic bacteria. Odors in wetwood ranging from rancid to a fetid rumenlike odor have been traced to bacterial metabolism of woody components, particularly extractives and hemicelluloses (I,187, 222, 223). Using potato mash media in the laboratory, the senior author (unpublished data) was able to reproduce the rancid, fatty acid odors of wetwood with pure cultures of Clostridium spp. isolated from wetwood of cottonwood, red oak, and white fir. Bauch et al. (20)- Eound acetic acid, propionic acid, and n-butyric acid present in the wetwood of silver fir, but not in the sapwood. They believe these fatty acids indicate a high bacterial activity in wetwood.

Hydrogen Ion Concentration or pH

The prevailing belief is that wetwood has a higher pH than normal wood. This can probably be traced to the publication, "Wetwood, Bacteria, and Increased pH in Trees," by Hartley et al. (E),who cite results indicating a higher pH in wetwood of many hardwoods and conifers. They cautioned, however, that not all wetwood is notably high in pH and that it is unsafe to assume that all wood with high pH is wetwood or has been.

10 A review of published data indicates that a Until additional studies are made we can comprehensive statement concerning the pH only speculate on the causes for of wetwood cannot be made now. Reported pH differences in pH between wetwood and values are generally on the alkaline side normal wood and between wetwood in for wetwood in hardwoods and on the acid individual trees and species. Microbial side for conifers, but there are exceptions populations in trees are possible causative between tree species and even within single agents, but they must be considered in species and trees. In comparison with conjunction with site and chemistry of the normal sapwood and heartwood, wetwood of trees. Seliskar (167) noted that elms on European aspen (Populus tremula L.) was poor sites had a1,kaline wetwood, whereas more acid (144), but wetwood in aspen from wetwood from trees on good sites was Minnesota can be either more acid or more acidic. From laboratory test cultures, alkaline (41, 67, 106). All wetwood in elm Carter (33)observed that the elm wetwood tested by Carter (33) was more alkaline bacterium, Erwinia nimipressuralis, will than a slightly acidic normal wood. turn a nutrient broth containing a sugar Seliskar (167) found that wetwood in elm strongly acid, but growth on nutrient broth can be either acid or alkaline, whereas the alone will result in an alkaline pH. Toole wetwood of Lombardy poplar (Populus niqra (191) reports that wetwood in eastern var. italica Muenchh.) was consistently on cottonwood growing along the Mississippi . the alkaline side. Wetwood in balsam poplar River between Vicksburg, Mississippi, and is slightly basic, the sapwood slightly Memphis, Tennessee, is neutral to alkaline, acidic, and the heartwood essentially and the sapwood is slightly acidic. The neutral (197). Rea heart, a type of senior author found similar acidic pH wetwood in paper birch, is alkaline values for sapwood of cottonwood growing adjacent to the acidic sapwood and turns along the Mississippi River in Wisconsin, acidic near the pith (31). Wetwood in but the wetwood had either higher or lower conifers is more acid than the adjacent pH values than sapwood. The composition of normal wood for California white fir (s,,the microbial population in wetwood varies -215), silver fir (20), and western hemlock with either acid or alkaline pH conditions (111). Another study of western hemlock for eastern cottonwood (222) and California reported that wetwood and normal heartwood white fir (see footnote 10) . Whether had a similar range in pH values from 4.1 differences in pH are the cause or the to 5.5 (165). Any increases in the pH of result of differences in microbial wetwood from conifers are small (79). populations has not been determined.

11 Anaerobiosis Strength Properties

Results from analysis of gas samples from There are conflicting reports in the wetwood in hardwood trees range from near literature concerning the relative strength anaerobic conditions in elm (33)and black properties of wetwood compared with normal cottonwood (93) to strictly anaerobic with sapwood and heartwood. Some investigators no oxygen present in eastern cottonwood found wetwood weaker than normal wood; (222)- . Carbon dioxide, nitrogen, and others report wetwood to be equal and even oxygen are the major gaseous components of greater in strength. We have found from normal wood, but oxygen was absent or in observations made in conjunction with very reduced amounts in the wetwood various tests on sawing, machining, drying, studied, indicating that any bacteria and mechanical strength properties that present must be either facultative or wetwood is often weaker than normal wood in obligate anaerobes. During the summer bonding strength of the compound middle growing season, high positive gas pressures lamella between wood cells. The secondary have been recorded in wetwood of standing wall of wetwood cells does not appear to be harawood trees, and these pressures are weaker than that of normal wood with attributed to bacterial metabolism (33, 79, similar specific gravity. Conflicting -191, --221, 222). Trunk gases contributing reports on the comparative strength to the positive pressures in wetwood are properties of wetwood can usually be carbon dioxide, hydrogen, methane, nitro- resolved by normalizing test results for gen, and hydrogen sulfide. Zeikus and Ward sample moisture content, sample size and (222) established that the methane gas is methods of preparation, and specific produced by an autotropic anaerobe which is gravity of samples. a secondary invader and not common to all wetwood populations even within the same host species. This methanogen, subsequently characterized and named Methanobacterium arbophilicum by Zeikus and Henning (221), is also found in soil and water. It can only grow under strictly anaerobic conditions and in the living tree only in wetwood where it metabolizes hydrogen and carbon dioxide produced by Clostridium and other anaerobic bacteria. Results from mechanical tests showing These other bacteria must, in turn, derive wetwood of hardwoods to be weaker than nourishment from the woody tissue. normal wood were all derived from the testing of green wood (40, 41, 80, 106, Van der Kamp et al. (93) consider wetwood -133); furthermore, the wetwood was usually with its near anaerobic conditions a lower in specific gravity than adjacent perfectly natural phenomenon that imparts normal wood. It is important that test resistance to decay to the inner wood of specimens be cut from dried wetwood rather black cottonwood trees. than from green wetwood and then dried; during drying, deep surface checks, ring failure, and internal honeycomb checks are much more likely to develop in wetwood than in normal wood. Lagerberg (117) and Thunell (189) found that Scots pine wetwood was weaker in bending, compression, and impact strength properties than were normal sapwood and heartwood. They attributed the

12 lower strength of wetwood to weakness of If specimens used in mechanical testing can the middle lamellae and seasoning checks in be prepared from dry, defect-free wetwood, the air-dried test specimens. Test speci- then strength differences between wetwood mens cut from green wetwood will not have and normal wood diminish. Stojanov and seasoning checks, but green wetwood is more Enthev (181) found that air-dried specimens likely to have tissue with weaker bonds from wetwood of silver fir were equal in , between cells than samples selectively cut static bending strength and stronger in from the defect-free portion of dried compression strength than was normal wood. wetwood blanks or boards. Toughness Table 3 shows that small test beams of strength of green wetwood samples from wetwood cut from kiln dried boards of white fir (212, 215) and from American and California white fir are as strong in slippery elm (167) was not significantly static bending properties as is normal lower than normal wood when differences in wood. Differences between strengths of

specific gravity were accounted for. , wetwood and normal wood were related to differences in specific gravity; however, during the preparation of the test specimens, many wetwood samples developed shelling failures and could not be tested. Table 3 also shows that sugar pine wetwood was weaker than normal wood even though higher in specific gravity.

Table 3--Comparison of specific gravity and mechanical stren th properties of normal wood and wetwood (sinker heartwood) from California white fir and sugar pine-17

\, Specific gravity oven Static bending strength properties/ dry weight, based on' Species and volume at test Stress at wood type Modulus of rupture Modulus of elasticity proportional limit

Mean Standard Standard Standard Standard deviation Mean deviation Mean deviation Mean deviation

12-percent moisture Pounds per Thousand pounds per ' Pounds per content square inch square inch square inch

White fir: Sapwood 0.353 0.012 9,601 787 1,313 90 5,968 611 Heartwood .343 .018 9,054 870 1,355 97 5,578 628 Wetwood .429 .072 11,329 2,347 1,649 3 38 5,997 1,253

Sugar pine : Sapwood .266 ,016 5,643 587 70 8 106 3,588 430 Heartwood .271 .024 6,049 702 686 87 3,883 491 Wetwood .281 .020 5,529 606 674 68 3,041 369

L/Test samples from kiln-dried lumber. Unpublished data from 3. C. Ward, U. S. Forest Products Laboratory, Madison, Wis. !/Strength values at 12-percent moisture content from test specimens measuring 1 by 1 inch in cross- section and 16 incnes along the grain (bending test over a 14-inch span).

13 The intrinsic weakness of wetwood in Ordinarily, sapwood will not develop ring cell-to-cell bonding strength appears to be shake and honeycomb, but these defects can related to the production of pectin- occur if sapwood is submerged and infected degrading enzymes by bacteria, especially by bacteria that produce pectolytic enzymes the obligate anaerobe Clostridium. These (180). Salamon (E)found that honeycomb enzymes degrade the pectic substances in and shake occurred in dried sapwood boards the compound middle lamella that holds from dead lodgepole pine and Engelmann together the wood cells. Wong and Preece spruce trees salvaged from flooded areas. (219) observed degradation of the middle He observed heavy concentrations of lamellae of cricket-bat willow by the bacteria in this sapwood under the electron facultative anaerobe Erwinia salicis which microscope and considered bacteria respon- also produces pectolytic enzymes. Soluble sible for the defects. Boards from sugars could not be detected in the wetwood sprinkled or water-stored Scots pine and of Abies alba, so Bauch et al. (20) assumed Norway spruce logs were also found by that pectinaceous compounds and hemicellu- Boutelje and Ihlstedt (26)to be more loses serve as substrates for wetwood liable to checking than boards from newly bacteria. Bacteria isolated from wetwood felled trees. A wide variety of bacteria, have not been found capable of degrading including anaerobic pectin-degrading lignin and cellulose or the secondary cell Clostridium spp., were isolated from wall under laboratory conditions (214, sapwood of water-stored Scots pine by 217). Furthermore, microscopic examination Karnop (95) but not from the heartwood. of wetwood indicates that secondary walls are not visibly degraded as are the walls of wood decayed by fungi or attacked by Permeability wood-destroying bacteria (2,106, 107, 117, 122, 130, 158, 164, 213). Hillis et Wetwood has long been considered to have al. (83)consider wetwood bacteria respon- low permeability because it is extremely sible for shake in trees. slow to dry and wet pockets are often present in dry lumber (79). Several Sometimes a strong, pectin-degrading studies have correlated slow drying of bacterium will be absent from the microbial lumber with restricted flow of liquids or population in wetwood and shake, deep gases through small cores of wetwood from checks, and honeycomb will not appear in aspen (98, 106), western hemlock (111, 120, the wood. For example, when American elm -121), and western redcedar (188) . On the wetwood was without Clostridium in its other hand, the absorptive capacity of microbial population, the wood did not wetwood can be greater than that of normal develop deep surface checks, honeycomb, or wood. In the green condition, white fir ring failure during kiln drying (24). wetwood is slow drying, but it will absorb American elm with wetwood infected by more oil than normal wood does after drying Clostridium is highly susceptible to ring (2, 215, 217). Air-dried wetwood from failure and shelling when subjected to Scots pine has greater water absorption drying and machining stresses and is capacity than normal wood and the capillary referred to as "onion elm" in the lumber rise of water is much more rapid, yet the trade. lumber will contain wet pockets with moisture content as high as 100 percent (117) The moisture-holding capacity of elm wetwood does not exceed that of normal woou (167), but elm lumber with wetwood does not dry abnormally slowly either (24).

14 For a better understanding of the total concept of permeability for wetwood, Chemical Brown Stain Precursors studies should be designed to evaluate the relative contributions of wetwood extrac- Dark discolorations or chemical brown tive, pit aspiration, tyloses, and bac- stains frequently develop on the surface of wetwood which, after being removed from the terial metabolism. Wetwood can have concentrations of extractives that not only anaerobic atmosphere of the tree, is exposed to aerobic or oxidative condi- may block cell lumens and pits, but can tions. The inten,sity of these chemicals or also have greater osmotic pressures than oxidative brown stains varies with wood normal wood (5, 45, 83, 106, 117, 2, 112, drying conditions, tree species, and -136, 139, 169). Reduced permeability 165, individual trees. Wetwood has been' of wetwood has been associated with aspira- associated with dark discolorations in both tion of bordered pits in softwoods (111, hardwoods and softwoods (2), particu - -121, -203) and tyloses in hardwoods (98, larly in these species: aspen (2,84, -106, 205). Bacteria have produced slime or 106,. 133) I white popular , eastern white extracellular polysaccharides in the -- (31) pine , western redcedar (136), redwood wetwood of both conifers and hardwoods (35) (2), western hemlock 165) , "Sugi" (158, 203, 205). Bacterial slime can (18, (Cryptomeria japonica (L.F.) D. Don) contribute to blockage of cells and (s), paper birch and sugar maple , and increased osmotic pressure. (2) cricket-bat willow (47, 209, 219).

Bacterial degradation of the normal wood sugars'and polyphenols may cause wetwood to develop dark oxidation stains when dried. Chemical brown stain has been attributed to the bacterial attack on extractives in sugar pine (182), western hemlock (g),and Pacific silver fir (19). The Forest Products Laboratory ' s (FPL) investigations (see footnote 8) found that the formation of chemical brown stain in freshly sawed In contrast to wetwood, the permeability of green lumber from California white fir, water-stored logs is increased, rather than sugar pine, eastern white pine, western decreased, by bacteria. Porosity of water- hemlock, aspen, and cottonwood is asso- stored wood is increased by bacterial degra- ciated with and confined to the wetwood dation and destruction of pit membranes and zones of these trees. This stain, however, thin-walled parenchyma cells, especially in did not develop uniformly in all wetwood of the rays (a,26, 50, 55, G, 72, 90, 94, these species; variations in composition of -95, 105, 119, 157, 195, 208). To a limited bacterial populations appear to be degree, cell walls in water-stored sapwood important, FPL data suggest that the may be pitted and corroded (44, 69, 70, 72, presence of phenyloxidizing bacteria -76, 119), suggesting that bacteria may be similar to those described by Greaves (70) attacking -the wood under aerobic rather is required before very dark chemical brown than anaerobic conditions. Karnop (E) stain develops in wetwood. found that the anaerobic Clostridium omelianski can attack unlignified cellulose in the sapwood of water-stored pine, but this activity is reduced with low water temperature and acidic conditions.

15 Timber Utilization and Wood Processing Problems

Chemical brown stain in wetwood is The presence of wetwood can cause sub- identical to the so-called sour log brown stantial economic losses when the affected stain that develops on the surface of timber is converted into logs and end-use softwood lumber sawn from logs stored under products. Since wetwood is usually limited water or in moist, shaded log decks. to inner sapwood and heartwood, it seem- Millett (141)observed that brown stain ingly is not detrimental to growth of precursors can be present in sugar pine trees. In trees where wetwood radiates trees, or the precursors can form by into the outer sapwood from the central enzymatic or hydrolytic degradation in core because of insect attack and other stored logs. Both types of brown stain may stem injuries, the function of sapwood may have similar biochemical origins. Bacteria be impaired. To what extent this may are considered factors in the formation of affect the growth of the tree has not been sour log brown stain on sapwood of western investigated. pines (55, 182, 183). Knuth (104)dis - covered that chemical brown stain, but not decay, will develop on the surface of wood samples submerged in liquid cultures of bacteria. Formation of stain was enhanced by autoclaving the wood before inoculation, and aerobic conditions were necessary for final development of stain. Evans and Halvorson (61) studied the chemistry of brown stain in water-stored sapwood and wetwood of western hemlock. From theif research, they were able to postulate that Shake and Frost Cracks bacterial enzymes (probably polyphenol oxidases) condense monomeric leucoantho- The weaker bonding between the cells of cyanins to water soluble polymers. These wetwood can result in radial and tangential polymers migrate to the wood surface during growth ring separations when the affected drying and on exposure to the atmosphere trees are subjected to stresses from wind, undergo oxidative condensation to dark growth, and freezing. These separations, brown polymers. known as shake (radial and ring) and sometimes spangles, are internal defects of the trunk that often go undetected when the tree appears vigorous and healthy. Shake can make boards with otherwise sound and clear wood, worthless for structural and factory grade lumber. The construction industry is the largest wood-using industry, and the losses in available construction grade lumber resulting from shake in both trees and boards are considerable.

16 Many logs, both hardwood and conifer, are excluded from the most valuable log grades for lumber and veneer only because they contain shake (a,117, 124, 125, 126, 127, -128) . Shake in western hemlock logs from Alaska has caused staggering losses in the volume of wood intended for export to Japan.=/ An association between shake and wetwood has been proposed by many investigators (2,33, 37, 2,83, 96, 110, -111, 117, 202, 203, 204). Even though Frost cracks on the outer stem surface wetwood is present in conjunction with much appear to be an extension of shake from of the shake observed in trees and logs, within the bole; they result not only in the actual formation of shake is a complex loss of usable wood volume but also in a process involving other factors, such as reduced yield of high quality lumber or tree growth stresses, stem injuries, and veneer from the logs. Wood from trees with anomalous wood tissue (38, 83, 91, 113, frost cracks is likely to contain wetwood -114, 115, 124, 129, 130, 140, 172, E). (see footnote 3) (46, 2,88, 117) . In European poplar plantations, frost crack is a common and serious defect consistently 15/R. 0. Woodf in, Pacific Northwest Forest associated with bacterial wetwood in and Range Experiment Station, Portland, affected trees (E,62, 82) . Surveys of Oreg., personal communication to J. C. Ward. defect in western conifers do not indicate a close relationship between frost cracks and fungal decay (27, e),yet frost cracks certainly offer a favorable infection court for decay fungi. Aho (2) found that less than 6 percent of the frost cracks in grand fir from Oregon and Washington were infected by fungi, and decay losses were small. He did find that all grand fir trees with frost cracks invariably had wetwood, and 46.7 percent of all trees 11.0 inches or more in diameter contained frost cracks.=/ From an extensive review of the literature, Schirp (163)- found that the association of frost cracks with wetwood in tree stems dated back to 1765.

16/P. E. Aho, Forestry Sciences Labor- atory, Corvallis, Oreg., unpublished data.

17 Rapidly freezing air temperatures are also necessary for formation of frost cracks. In Macedonia, frost cracks developed in the stems of poplars (Populus x euramericana (Dode) Guinier) growing in an area with a continental climate (warm summer temperatures and cold oscillating winter temperatures), but not a single stem crack was observed on trees growing in an area with a Losses in product volume and value asso- Mediterranean climate (mild winters and hot ciated with shake and frost cracks are summers) (74). Robert Hartig (77)I the especially important because these defects 'If a the r I' of forest pa tho logy, observed are most prevalent in the lower two logs of frost cracks to be most abundant on the trees and, in many instances, are spiraled northeast side of trees where sudden and (see footnote 3) (163, 196) . In the true large drops in temperature often occurred firs, for example, these logs have the in winter. He also noted radial and potential for producing not only the peripheral cracks in the interior of old highest quality boards but also nearly half oaks; these cracks did not extend outside the total lumber volume of the tree (215). the stem, and he was uncertain whether they It is in these logs that reducing wetwood- were due to frost. A survey of damage from related losses has its greatest potential, frost cracks on walnut (Juqlans reqia L.) both in volume and value (147). The growing in the Ukraine showed that the occurrence of combinations of shake, frost number of stems affected ranged from 1.1 crack, and spiral grain in white spruce to 83.4 percent in stands on south timber growing in northern Alberta seri- slopes with fairly moist soils (E). ously affected the yield of 1- and 2-inch White fir stands of the Sierra Nevada in dimension lumber (131). Shake caused 7 to California have two to three times more 12 percent of the lumber output per tree to frost cracks in trees on the east slope be graded utility or lower. Degrade was with greater drops in temperature than on higher, 15 to 22 percent, when frost cracks the milder west slope (196). Freezing of were present; and trees with both frost redwood boards results in breakage of cracks and spiral grain suffered the heartwood with wetwood but not with normal highest grade losses--23 to 26 percent. heartwood below 150-percent moisture content (58).

18 Checking and Collapse The dry kiln operation is often blamed for shake in dried lumber. Results from investigations with softwood dimension lumber reveal, however, that much of the observed shake was initiated in the tree and only became apparent after drying (37, 87, 140, -203). Shake in western hemlock lumber has been associated more with wetwood than with drying conditions (111, 203) .

The unexpected occurrence of checking and collapse in lumber and veneer during drying can be attributed to the same weakening of the compound middle lamella that predis- poses the wood to shake and formation of frost cracks in trees. In wetwood, drying checks can develop in both a radial and a tangential direction. Radial checks may be deep surface checks, internal ruptures called honeycomb, or bottleneck checks-- Green lumber with wetwood is more likely to deep surface checks that develop into a develop collapse during the early stages of honeycomb. Tangential checks known as ring drying than lumber with normal sapwood and failure appear to be an incipient form of heartwood. Collapse can be expected in ring shake that starts in the tree: these wetwood when the bonding strength between checks do not actually rupture until cells has been weakened and the rate of subjected to shrinkage stresses (E).A internal moisture loss through cell description by Kutsche and Ethington (116) cavities is restricted. A generally held of various shelling failures during the theory is that collapse can develop only in machining of wood suggests that some cell cavities that are completely saturated failures may be related to wetwood and may with water (142) , but Kemp (98) was able to possibly be an incipient form of ring induce collapse in wetwood cells of aspen shake. Collapse is essentially a col- that were not completely saturated. He was lective internal failure of cell walls also able to relate collapse to portions of resulting in depressions on the surface of the board with the lowest rates of moisture the dried board or veneer which cannot loss. Honeycomb and ring failure are often always be removed with surfacing. Figures associated with collapse in wetwood. 1 and 2 show examples of honeycomb, ring Reconditioning of collapsed lumber by failure, and collapse that developed in steaming is possible when internal ruptures wetwood during drying. Deep surface checks are not present (108) . are present in some pieces but are not visible because they close up toward the end of drying when the surface is below 25-percent moisture content (MC) while the core is still above 30-percent MC.

19 Figure 1 .--Cross-cut sections from softwood boards with wetwood that developed collapse (C)I honeycomb (HC), and ring failure (RF) in drying: A, old-growth eastern hemlock: B, young-growth eastern hemlock: C, old-growth western hemlock: D, young-growth western hemlock: E, California white fir.

20 A D

B E

C F

Figure 2. --Cross-cut sections from hardwood boards with wetwood that developed collapse (C) I honeycomb (HC) , and ring failure (RF) in drying: A and B, northern red oak; C, eastern cottonwood; D, red maple; E, American sycamore: F, largetooth aspen .

21 Two major sources of stress considered responsible for collapse during drying are liquid water tension produced by capillary forces in the cell which can be very high with rapid drying and compression stress perpendicular to the grain caused by a sharp moisture content gradient across the board (108, 142, 151). Little information The severity of honeycomb and collapse in is available on the comparative wetwood usually increases with an increase susceptibility of wetwood and normal wood in temperatures during the early and middle to collapse. Kemp (98) found that aspen stages of drying. Temperatures at which heartwood, artificially saturated with these defects begin to form in wetwood water, will collapse but only at a higher apparently vary with tree species, site temperature than that required to first conditions, and types of wetwood. When initiate collapse in wetwood. High drying green lumber is kiln dried, honeycomb in temperatures can plasticize wood and make the wetwood of California black oak and it less able to withstand the stresses northern red oak can be minimized by lower associated with collapse (108) . Thin- initial dry bulb temperatures (202, 205). walled cells in the newly formed earlywood Wetwood in southern bottom-land oaks, of outer sapwood have collapsed when the however, honeycomb and collapse under the living tree is subjected to extreme mildest kiln schedules; this lumber must moisture stress (198). Results from drying initially be dried in the open air or tests at the Forest Products Laboratory dried in kilns at low temperatures to at (see footnote 8) indicate that wetwood is least 25 percent MC before it can be kiln susceptible to collapse under kiln-drying uriea.l8/ Collapse in aqen wetwood can temperatures less than 212OF, but normal be reduced by using mild kiln conditions wood is not. in the early stages of drying (2). Western redcedar lumber containing a Collapse, honeycomb, and ring failure are particularly dark heavy type of wetwood costly defects associated with the drying will sometimes collapse after only 1 day of of wetwood from white firg/(145) , air drying.=/ With high temperature western hemlock (100) , redwood (138)- , kiln schedules (temperature of 212OF or western redcedar (a,73, 188), aspen (41, higher) most wetwood will honeycomb or -98, 133, 134) ,and west coast hardwoods collapse, but usually adjacent normal wood (176)- -particularly Pacific madrone (30), will not?!?/(S, 132, 134, 159). tanoak (154), and California black oak (205).- The plugging of cell cavities with tyloses increases the tendency of wetwood -!?./Don Cuppett, Northeastern Forest to collapse in such hardwoods as aspen Experiment Station, Princeton, W. Va., (g),overcup oak (126), California black personal communication to J. C. Ward. oak (205), and red gum (151) . =/Jack McChesney, Louisiana Pacific Corp. , Dillard, Oreg. , personal communication to J. C. Ward. 17/B. G. Anderson. Study of change in grade and footage loss in kiln dried white g/Unpublished data from drying studies; fir lumber from the green chain to the on file at U.S. Forest Products Laboratory, car. Report presented at the meeting of Madison, Wis. Eastern Oregon-Southern Idaho Dry Kiln Club, La Grande, Oreg., Nov. 19, 1954. 4 p. Oregon Forest Products Laboratory, Corvallis, Oreg.

22 Honeycomb and ring failure are major Slow Drying Rates and defects associated with kiln drying of oak, Uneven Moisture Content our most important hardwood.lumber species. Annual wood losses from drying defects associated with wetwood in oak factory grade lumber produced in the Eastern United States are estimated to be at least 3 percent. It is not unusual, however, for 10 to 25 percent or even half the lumber charges from individual kilns to be lost because of honeycomb and ring The wetwood of many species has low failure . permeability and requires much longer drying times than normal wood to reach a FPL studies on kiln drying northern red oak desired moisture content. Even when lumber, green from the saw, showed 8- to wetwood boards reach the desired average MC, 25-percent losses in volume from honeycomb there is an uneven distribution of moisture and ring failure in wetwood (201). Mone- where the shell is very dry but the,core tary losses ranged from $34.28 to $139.42 contains wet pockets or streaks that are per thousand board feet of rough dry still above the fiber saturation point. lumber. Three studies of kiln drying Sometimes after supposedly dry wetwood California black oak at a commercial (E) lumber is surfaced, the internal wet mill showed losses from defects in wetwood pockets dry and collapse, resulting in to be 7 to 48 percent of the total volume degrade of the lumber (134). Wet pockets of Number 1 Common and Better lumber. can be a problem when dried wetwood from Total monetary loss in rough, dry lumber aspen and hemlock are used for core stock for the three studies was over $9,000. in the manufacture of doors and panels. ' This can explain why one large Los Angeles Although these wet pockets may be pencil lumber company fills a standing monthly thin, they will build up enough steam order for one-half-million board feet of pressure during electronic gluing opera- 4/4-inch kiln-dried oak lumber with oak tions to explode and shatter the surface of imported from the Eastern United States. the pieces.a/ Internal wet pockets in kiln-dried western hemlock causes erroneous Smith (180) estimates that, for British determinations of MC when electronic meters Columbia, the development of honeycomb and are used (109). ring shake in softwood studs with bacterially infected wood will result in a reduction in grade of $7 per thousand board =/ Elmer Cermak, Algoma Hardwoods, Inc. , feet. We can calculate from the average Algoma, Wis., personal communication to J. grade prices in "Random Lengths" (150) that C. Ward. drying defects associated with wetwood can cause grade losses of $38 to $40 per thousand board feet for hem-f ir dimension lumber.

23 A serious economic problem can result from the presence of impermeable wetwood in softwood dimension lumber for construction purposes. The same problem applies to aspen and poplar studs and light framing lumber graded under softwood rules. To meet moisture specifications for kiln-dried lumber softwood dimension lumber must be dried to at least 19-percent MC; the desir- Table 4 shows that the slow drying rates of able range is 12 to 16 percent. Boards wetwood vary with tree species. Wetwood with wetwood may require 50 percent or more from aspen and the conifers is much less time in the dry kiln to reach 19-percent MC permeable than normal wood, whereas wetwood as do boards with sapwood and heartwood. from cottonwood, elm, and oak takes only When the volume of boards exceeding the slightly longer to dry than normal wood. 19-percent MC specification is greater than The effect of wetwood on reducing drying 5 percent, a kiln charge or shipment of rates tends to decrease as thickness of kiln-dried lumber is considered to be in boards decreases. For some species, the noncompliance with specifications for time required to dry veneer containing moisture?-?/ (2,178, 210, 218). wetwood and veneer containing sapwood differs little for a given MC; but for Slow drying of construction lumber con- species such as red gum, true firs, taining wetwood can be expected for these hemlock, larch, and redwood, there are softwood species: redwood (103, 138, 151) , decided differences (126). A comparison of true firs (101, 103, 145, 151; also see drying times for green veneer from balsam footnote 17); western hemlock (2,103, fir and white fir (table 5) indicates that -110, z),western redcedar (2,103, 151, wetwood has an adverse effect on drying -159), and white pines (151). Hardwood rates for even thin material. species with impermeable wetwood and slow drying rates are: aspen (36,3, 133, 200) , Where wetwood boards occur in kiln charges red gum (151) , and water and swamp tupelo of softwood and aspen dimension lumber, the (137).- Redwood with heavy sinker heart is processor is confronted with five possible especially difficult to dry (138), and alternatives; each may result in losses of 1-inch-thick boards require 146 days of air wood and energy and in higher manufacturing drying to reach 20 percent MC (52). In costs. contrast, 2-inch-thick redwood with light and medium heartwood can be air dried to 1. The kiln residence time can be extended 19-percent MC in 74 days (8). Arganbright until the wet test boards reach the and Dost (2) found that development of required 19-percent MC. This can cause chemical brown stain decreases the drying overdrying of nonwetwood stock (i.e., below rate of sugar pine and, at the end of 11-percent MC), which is then subject to drying, retards moisture movement back into planer splits and costly degrade in subse- the board surface during conditioning quent machining operations (100, 101, 103, treatment. --110, 145, 218; also see footnotes 17 and 22). GIG. Reinking. 1971. Kiln drying lumber to the moisture provisions of the new lumber standards. Forest Products Research Society News Digest File J-1.1, 2 p. Madison, Wis.

24 Table 4--0rying times for green wetwood boards compared with drying times for boards containing normal wood/

Initial kiln Board specifications temperatures!/ Wetwood Sapwood Heartwood

Species Source of data Dried Green Green Green moisture moisture Drying moisture Drying moisture Drying Thickness content DB WB content time content time content time -Inches -Percent - - "F------Percent Hours Percent Hours Percent Hours Softwoods: Western hemlock Ward and Kozlik (203) 1-34 15 180 176 150 139 156 82 54 59 Western hemlock Kozlik et al. (11' 3/4 10 100 69 153 170 -- -- 66.1 90 Eastern hemlock J. C. Ward31 1-3/4 15 180 170 148 185 137 95 75 96 White fir Smith and Dittman (177) 1-7/8 20 160 145 193 158 145 84 57 42 White fir Smith and Dittman (177) 1-7/8 4/15 160 145 193 3/195 145 -4/97 57 4/63 White fir Pong and Wilcox (kr 1- 1-3/4 17-16 160 140 -- 174 -- 106 -- - 60 White fir J. C. Ward?/ 1-3/4 15 180 170 155 150 170 105 66 73 Sugar pine J. C. Ward?/ 1-1/2 15 120 3/75 194 226 204 148 51 72 Hardwoods:$/ Aspen Cech (36), Huffman (E) 1-3/4 15 140 133 170 3/210+ 140 175 -- -- Quaking aspen J. C. Krd 200) 1-3/4 15 180 170 115-128 179 76-122 90 81-106 115 Eastern cottonwood J. C. Ward+ 1-1/8 7 180 170 144 75 131 85 -- -- American elm J. C. Ward31 1-1/8 7 120 113 106 134 90 121 69 113 California black oak Ward and Shi'6dd (205) 1-1/8 7 120 115 95 387 -- -- 85 379 Northern red oak J. C. Ward31 1-1/8 7 125 121 ' 97 324 -- -- 86 312

1_/Comparisons are within kiln runs and not among kiln runs or between species. /DEI = dry bulb temperature; WB = wet bulb temperature. ?/J. C. Ward, unpublished data on file at U.S. Forest Products Laboratory, Madison, Wis. '/Extrapolated from published data. ?/Kiln vents open with steam sprays off. 6/A11 wetwood developed honeycomb, collapse, or ring failure or a combination of these.

Table 5--Drying times for green veneer with wetwood compared with veneer containing normal sapwood and heartwood

Veneer specifications Wetwood Sapwood Heartwood Species Source of data Dried Dryer Green Drying Green Drying Green Drying Thickness moisture temperatures moisture time moisture time moisture time content conten ti! content3 cont en $1

-Inch Percent OF Percent Minutes Percent Minutes Percent Minutes Balsam fir Dokken and Lefebvre (48) 1/10 4 300 154 18-1/2 201 15-1/4 76 11 Dokken and Lefebvre (m> 4 450 154 7,3/4 201 7-1/4 76 5-1/2 Dokken and Lefebvre (m) 1/6 4 300 154 35 201 31 76 25-1/2 Dokken and Lefebvre (48) 450 154 15 201 14-1/4 76 9-1/2 White fir Vern Parker21 1/8 5 -3/ 150 10 150 8 -- -4/

1/Average value.

/Superintendent, Plywood Mill, Bendix Corp., Martell, Calif. , personal communication to W .3 Y. Pong . Zll-stage gas jet-dried: 4500, 4500, 4000, and 35OoF. $/Heartwood dried according to sapwood schedule of 8 minutes will be overdried with a moisture content of 1 percent.

25 2. The wet stock can be sorted and redried Table 6-Freight costs for shipping white fir lumberl/ after a normal kiln run. This approach Cost of shipping 1,000 board feet will increase drying and handling costs for Moisture content Calculated TO Los Angeles To Chicago weight per 1,000 (base rate, (base rate, the wetwood lumber. For white fir board feet $1.27/100 pounds) $3.07/100 pounds) dimension lumber containing wetwood, redrying can result in a 40-percent 0 1,271 16.14 39.02 12 1,423 18.07 43.69 increase in the kiln-drying costs.Z/ 15 1,463 18.58 44.91 19 1,513 19.22 46.45 25 1,590 20.19 48.81 75 2,226 28.27 68.34 100 2,543 32.30 78.07 3. Boards greater than 19-percent MC can be 115 2,734 34.72 83.93 150 3,178 40.36 97.56 marketed as surfaced green lumber and less 11F.o.b. Portland; base rates (Oec. 15, 1978) are for railroad shipnents of 85,000 return will be received for the product. pounds or less (Western Wood Products Association, Portland, Oreg.). For hem-fir dimension lumber, this can amount to approximately $26 per thousand board feet in selling price (149), not to mention drying and extra handling losses. Shipping weights and the resulting shipping costs of green lumber are important considerations in this third alternative. In table 6 are calculated weights for 1,000 board feet of white fir at different moisture contents. Also included are costs for shipping this lumber to Los Angeles and Chicago from Portland, Oregon. The price differential of $26 between green and dry lumber barely offsets the shipping cost 4. The lumber can be dried by a normal differential of dry lumber (15 percent) and schedule and not sorted for wet stock. All green lumber (150 percent) to Los Angeles boards, both above and below 19-percent MC, but not to Chicago. would be surfaced and sold as kiln dried. This option could be exceedingly costly if the volume of wet stock exceeded the GlDonald 0. Prielipp, general manager, 5-percent limitation (210) and was detected Roseburg Lumber Co., Anderson Divisiori, by the buyer and reinspection by the Anderson, Calif., personal communication to grading association requested. Not only J. C. Ward. woula the surfaced lumber have to be resorted, regraded, and metered for moisture, but the boards that exceeded the maximum allowable moisture would be considered substandard surfaced green and regraded accordingly. Losses in excess of $50 per thousand board feet are possible with re inspect ion .

26 5. The green lumber could be segregated Another obstacle to obtaining maximum into uniform drying sorts (sapwood, effectiveness in presorting is the mixture heartwood, and wetwood or sinker) and each of wetwood and normal wood that occurs in then dried under different kiln schedules many boards on the commercial green chain or treatments. This presorting would (110,147). It is possible to develop minimize the extremes in final moisture optimum schedules for drying boards having content within a given kiln charge and has mixtures of normal sapwood and heartwood long been advocated for western softwoods with wide differences in green moisture (103, 178), particularly white fir*/(lOl, content (161), but not for mixtures of -177, 179; also see footnote 17), western sapwood and wetwood even though there may hemlock (110), redwood (138), and be little or no difference in green incense-cedar (152). Presorting would moisture content (162). Studies of white minimize energy costs. With the energy fir indicate that boards containing crisis, it becomes imperative that costs of mixtures of wetwood, sapwood, energy used in drying and redrying wetwood and corky heartwood will have more drying be given careful consideration, especially and surfacing problems than boards that dry since 60 to 70 percent of the total energy more uniformly (147, 215). used in manufacturing most wood products is consumed in drying (43). Steaming of green lumber before drying increased the drying rate of wetwood from Commercial presorting of green lumber for white fir (175) and redwood (52),- but was drying by visual detection and hand methods not effective with western hemlock (110) or has been used with some success for western eastern hemlock (see footnote 8). The hemlock (110) , incense-cedar (152) , and chemical nature of extractives in the California white fir (145, 178, 215). For wetwood seems to be an important factor presorting to be effective, however, each controlling the effectiveness of board must be examined on all sides during presteaming. the segregation operation. Under high production mill conditions, manual presorting is generally not possible. Examination of individual boards will also be limited where tray and drop sorters are used. Mechanical, electrical, and optical instruments for automatic presorting of wetwood lumber on a commercial scale have not been developed (207) . d

24/5. Steel. 1953. Kiln drying white fir. Wood drying committee news digest. (Aug.) 3 p. Forest Products Research Society, Madison, Wis.

27 rown Stain Brown stain can develop in both air-dried and kiln-dried wood, but it is usually more pronounced under warm, humid kiln Chemical brown stain in wetwood is an schedules. Considerable brown stain can especially serious defect in lumber, occur in boards air dried at temperatures veneer, and wood fiber products graded on as low as Chemical brown appearance. Brown stain also affects the 8OoF (E). stain may also develop just below, but not marketability of softwood dimension lumber on the surface of, air-dried lumber and because consumers think the wood looks will not be noticed until after the boards decayed. Wood decay fungi are not considered causal agents for chemical brown are surfaced (155). This concealed brown stain, referred to as yard brown stain, has stain 56, 103, 148, 151). Brown (51, 85, been observed in ponderosa pine, sugar stain in wetwood usually develops in the pine, and the white pines Wetwood zone between sapwood and heartwood or (E). prone to developing brown stain should be within bacterially infected heartwood. segregated from other green lumber. The Sapwood of many species develops brown wetwood stock would be air dried; the stain if taken from logs stored for an normal stock, kiln dried. For minimum extended time under humid conditions. development of brown stain during air Brown stain developed in eastern white pine drying, the lumber should be from freshly lumber from logs stored in the woods for 42 felled trees and drying should be fast, with and 93 days, but not in lumber sawn and seasoned within 24 hours of felling (E). relative humidities below 65 percent (E, Depth of stain in boards increased as -61, 66, 141, 155) . storage time increased. Extended storage If faster drying of wetwood is desired or of ponderosa pine and sugar pine logs under presorting is not feasible, reduction or water sprays will initiate development of prevention of chemical brown stain during brown stain in sapwood boards and further kiln drying may be accomplished by either intensify darkening in wetwood zones.25/ manipulating kiln schedules or dipping the Timber species noted for developing green boards in enzyme-inhibiting or antioxidant solutions. There are, however, chemical brown stain during drying drawbacks to these preventive methods that usually tend to have wetwood. Processing are important. problems associated with chemical brown stain in lumber are considered important commercially for the following species: sugar pine, eastern and western white pines, ponderosa pine, Pacific silver fir, noble fir, western hemlock, redwood, western redcedar, and Sitka spruce (5, 1, -18, 19,=, 2,35, 56, 61, 89, 99, 103, -141, 151, 165).

25/Del Shedd, Quality Control Supervisor, Kimberly Clark Corp., Anderson, Calif . , personal communication to J. C. Ward.

28 m'w initial temperatures in kilns and low Dipping green lumber in enzyme-inhibiting humidities with good air circulation are or antioxidant solutions usually prevents necessary to successfully reduce brown brown stain and permits higher initial kiln stain or prevent it (23,2, 99, 102, 105, temperatures and humidities (34,35, 61, -141) . Rosen (156) found that high -102, 103, 170, 182). Such reagents will temperature jet drying eliminated brown not reduce brown stain if they are not able stain in cottonwood, but the wetwood to sufficiently penetrate the wood surface collapsed and checked. With low during the dip treatment (141) . Proper use temperatures, the kiln usually has to be of antistain dips results in substantial vented to attain low relative humidities reductions in drying and energy costs, but (29, 102, 103). Venting dry kilns results most chemicals used are highly toxic to in a great waste of energy. Sometimes the humans. Because of Occupational Safety and kiln doors must be opened during drying to Health Administration inspections, the lower the humidity, and the duration of the dipping of boards in brown stain retardant venting can be from 3 days to 1 week. solutions has been discontinued by many Manipulating kiln schedules, has not been mills. successful in controlling dark stains in redwood unless the lumber was first steamed Stain-producing extractives from wetwood (5, 52, 2). Solvent drying of redwood can cause problems with finishes. Figure 4 with acetone has been proposed for shows the undesirable darkening of a elimination of stains (a). lacquer finish from an underlying oak laminate containing wetwood. Water-soluble extractives in wetwood of redwood and western redcedar cause serious problems when stains penetrate finishes on exterior siding. Connors found that extraction of sequirins from the redwood can effectively prevent the problem.26/ On a commercial scale this treatment could be cumbersome with lumber, and a disposal problem would Kiln schedules to prevent stain are not be created. Connors also found that always successful if the drying operation dipping the boards in lead acetate before is regulated either on a time basis or on applying finishes is effective but kiln samples containing only normal wood. expensive, and lead is now prohibited for Figure 3 shows chemical brown stain that such use. developed only in sugar pine boards containing wetwood but not in sapwood,or The chemical precursors causing brown stain normal heartwood. These boards were dried problems in drying wetwood in western under an antistain schedule based on the hemlock lumber are also responsible for average drying rate of boards with normal problems when this 'species is used for wood. The operation could have been based ground woodpulp (15,17). The cost per ton on the drying rate of the wetwood boards, of raising the brightness of the ground but the normal boards would have been over- hemlock woodpulp can be increased by 15 to dried and the _subsequent surfacing of these 20 times when brown stain occurs. Aspen boards would result in planer splitting. wetwood is objectionable for pulp because The solution is to segregate the normal of added bleaching costs (79). boards from the wetwood boards and then dry each board sort under different schedules. GIG. L. Connors. 1968. Considerations for reducing extractives staining in redwood. Office report, 11 p. U.S. Forest Products Laboratory, Madison, .Wis.

29 Figure 3.--Kiln-dried sugar pine shows chemical brown stain in center board that contained wetwood but not in boards with sapwood (left) or normal heartwood (right). End sections (top) were cross cut fromrough , dry boards, and one-sixteenth inch was planed from board surfaces (bottom).

30 Figure 4.--Darkening of a white lacquer finish overlying a kiln-dried red oak laminate containing bacterial wetwood. Ring failure (RF) within the laminate extended to the surface during air drying of the lacquer finish. P lywood and Reconstituted The effect of wetwood on the strength of the glue bond is usually associated with B oards wet pockets, and there is a dearth of information on the influence of extractives Little is known about the effect of wetwood and pH. Poor adhesion because of uneven on the quality of plywood and reconstituted distribution,of moisture in dried veneers wood products. We believe that investiga- containing wetwood has been reported for tions of the use of wetwood in these eastern cottonwood (191), western hemlock products may well provide insight on (B),balsam fir (32), and white fir unsuspected causes of some processing (126). Oxidation stains are objectionable problems. Also, these products are characteristics for face veneersp and these increasingly promoted for use as components stains may possibly interfere with proper in light frame construction (184), and the adhesion of the glue to the wood. Some effect of wetwood on strength properties wetwocd species most susceptible to should be investigated. oxidation stains during production of plywood are: sugar pine, western white pine, ponderosa pine, Jeffrey pine, red maple, tanoak, bottom-land oaks, tupelo, and willow (126) .

A small amount of research data exists to suggest that wetwood may lower the strength properties of reconstituted boards that include particle board and hardboards. Table 7 shows that wetwood from aspen and western larch will not make as strong a There are several ways that wetwood causes flakeboard as normal sapwood and problems with the processing and quality of heartwood.281 Linear stability was not plywood. Shake and frost cracks cause adversely affected by wetwood, but "spinout" of bolts on the lathe, resulting thickness swelling was greater for aspen in splits and splintering of veneer (2, boards containing wetwood and least for -79, 125, 126). Commercial experience larch. Wet process hardboards from aspen indicates that wetwood in "sinker" logs of wetwood have a lower modulus of elasticity, species like redwood is undesirable for modulus of rupture, and internal bond veneer because of cutting and drying strength than boards from sapwood (67). problems (125). The assembly-time Dimensional stability of the hardboards tolerance of conventional plywood adhesion from wetwood was greater than boards from restricts the moisture content of veneer to sapwood, however. defined upper and lower limits. Control of moisture content in veneer from wetwood is a major technical problem and can lead to 2815. C. Ward and J. Chern. 1978. "undercured," "washed out," or "starved" Comparative properties of flakeboard made glue lines and to "blows" and "blister" in from normal wood and from bacterial wetwood the pressing operation (32). Nearly all of trembling aspen and western larch. A the "blows" during production of white fir preliminary report. 6 p. U,S. Forest plywood are related to wetwood in the Products Laboratory, Madison, Wis. veneer ..El

Z/Vern Parker, Bendix Corp. , Martell, Calif., personal communication to W. Y. Pong .

32 Table 7--Physical and mechanical roperties of 1/2-inch-thick flakeboarddl from normal wood and wetwood of trembling aspen and western larck/5

spec if ic g r av it y.l/ Mechanical properties Swelling in 30- to 90-percent Species and relative humidity type of wood Solid wood Flakeboard Moisture Modulus of Modulus of Internal content rupture elasticity bond Linear Thickness

Thou sand Pounds per pounds per Pounds per Percent square inch square inch square inch Percent Percent

Aspen (Wisconsin): Sapwood 0.474 0.657 7.2 5,541 692 128 0.07 6.88 w etw oo&/ .504 .652 7.4 4,499 618 95 .08 9.58 Aspen (Colorado) : Heartwood .35 .715 ' 6.2 6,390 994 76 .14 9.56 wet w oo&/ .34 .634 6.8 4,335 677 48 .14 12.76

Larch: Sapwood .480 .652 9.3 4,992 655 89 .09 11.45 Heartwood .454 .648 8.9 4,520 635 112 .10 9.87 w etwoo&/ .701 .628 9.2 3,542 549 74 .08 7.80

LIBoards made from 0.02- by 2.0-inch flakes with 4-percent phenolic resin. 2/Data from J. C. Ward and J. Chern. 1978. Comparative properties of flakeboard made from normal wood and from bacterial wetwood of trembling aspen and western larch. A preliminary report. 6 p. U.S. Forest Products Laboratory, Madison, Wis. z/Specific gravity of wood based on ovendry weight and ovendry volume. Specific gravity of board based on ovendry weight and volume of board at mechanical test moisture content. !!/Bacterial wetwood formed where sapwood changes to heartwood. /Bacterial wetwood formed in previously developed, normal heartwood. /Formed from microbially infected inner sapwood--heavily saturated with water-soluble extractives that included arabinogalactans.

Corrosion of Kilns

Reports of accelerated corrosion of dry considerably increases the liability of kilns have increased in frequency in recent wood to evolve corrosive acid vapors (10, years. Most cases of corrosion can be -11, 39). Use of high temperature schedules traced to highly acid atmospheres within in drying green wood increases corrosion. the kiln during drying. Not only are metal Contact between dissimilar metals in the walls, pipes, fasteners, etc. , attacked by kiln, such as aluminum and iron in an this corrosive mixture of air, but acidic atmosphere, will produce a "battery unprotected concrete (16)and wood stickers effect" and corrosion of metal will be are also subject to accelerated greatly accelerated (16). The drying of deterioration. Several explanations can be wood treated with aqueous solutions of given. Drying charges of green lumber preservatives will cause corrosion problems rather than partially air-dried lumber (2)

33 Research Needs

Although investigations are needed, we Wetwood is responsible for substantial believe that the presence of wetwood in losses of wood, energy, and production green lumber charges can be a definite expenditures in timber-using industries. factar in many reported cases of increased There is a clear need to more thoroughly kiln corrosion. Oak, hemlock, and the true assess these losses and to find ways of firs are species likely to have wetwood eliminating or minimizing them. with a pH as low as 3.5. Metal corrosion is greatly accelerated by a pH of 4.0 or An effective research program on wetwood less (10,11) , and acidic vapors of pH 3.5 should include planning short- and will attack concrete (16). Barton (16) long-term solutions to the overall problem related the presence of normally occurring and providing for them. Solid wood chelating compounds in the extractives of products, particularly lumber and veneer, western redcedar with the corrosion of iron are most adversely affected by processing but not of aluminum in dry kilns. Not all defects related to wetwood. Lumber and charges of western redcedar caused veneer are expected to be prime economic chelation corrosion. products from future timber harvests (E). In the long term, the best solution to the Wetwood in western hemlock lumber may be an wetwood problem may well result from timber important factor in kiln corrosion. In management research to prevent future 1951, MacLean and Gardner (135) reported occurrences of wetwood. that an increase in the deterioration of wooden dry kilns was due to increased use for drying western hemlock lumber. An acid Short-Term condensate of aqueous vapors from the hemlock resulted in deterioration of the The initial research effort must be cellulose in kiln boards and corrosion of primarily concerned with attacking existing metal fittings. Although Douglas-fir utilization and processing problems, but it heartwood is acid, the vapor condensates should also provide a scientific basis for were not as acid as those from hemlock. long-term research planning.? A short-term Also, Douglas-fir heartwood has a higher research program should concentrate on: (1) content of resin, and the vapor condensates assessing the occurrence of wetwood in form a protective layer. The acid vapors standing timber and its effect on product from drying one or two charges of hemlock yields and losses, (2) defining the will remove this protective layer of chemical and physical properties of wetwood Douglas-fir condensates. Most lumber is as a basis for detecting and segregating now dried in metal kilns, and Barton (16) affected wood products, and (3) developing estimates that at least 90 percent of the optimum utilization and processing methods corrosion in these kilns is caused by vapor for timber and wood products containing condensates. wetwood. Item 1 would be the pivotal area of endeavor for the short-term research program and also the area most likely to provide continuity with long-term research.

34 These studies should be carried out The major reason the wetwood problem is not cooperatively by timber managers, timber publicized is that most foresters and many processors, and forestry researchers. The wood processors have not related defects-- managers would provide the timber and the such as shake and frost cracks in trees and mill operators the processing facilities. collapse and honeycomb in lumber--to wetwood. Researchers would record information on This is understandable because, until just timber quality for selected sample trees. recently, wood scientists have related the Bucked logs from the sample trees would be unexpected occurrence of honeycomb and ring followed individually through the milling failure when drying wetwood lumber to an process and information, including the inherent and perfectly normal variability in grade and amount of product cut from each wood properties (75). Thus, lumber grading log, tallied. The yield data would be associations have been reluctant to compiled and analyzed in conjunction with recognize wetwood as a precursor to timber quality data to provide the basis processing defects when even scientific for predicting the product yield from experts are often unable to discern it in similar timber. Measurements of wetwood in green lumber. In fact, there appears to be the timber and the resultant defects in more recognition of wetwood and its problems both green and dried wood products would be by sawmill and dry kiln operators and incorporated into the beginning and final furniture manufacturers than there is in the phases of a product yield study. scientific community.

Studies on timber products and yields are Logical species for the initial short-term important to the initiation of research on studies are western hemlock, western true wetwood. Now we can only guess, but with firs, eastern oaks, and the white pines, some confidence, that the utilization and including sugar pine. These species are processing problems associated with wetwood very susceptible to formation of wetwood are costing the wood-using industries many and constitute a sizable volume of timber millions of dollars annually.. No on commercial forest lands in the United statistical or economic surveys have States (E,193). Comparisons of these been initiated either for the purpose of species with other commercial species are determining the amount of wetwood in timber shown in table 8. In spite of their stands or for estimating the losses that susceptibility to wetwood, western hemlock, unquestionably result from the processing of western true firs, eastern oaks, and white wetwood timber. Government agencies have pines are tree species of high value and not initiated and carried out the necessary capable of producing valuable lumber items surveys on wetwood because they are not (table 9) . aware that a problem exists; this stems largely from industry's reluctance to make a concerted effort to publicly recognize the problem.

35 Table 8--Comparison of softwood and hardwood timber volumes from USDA Forest Service (E),and susceptibility of species to formation of wetwood

Saw t imb er vo lume Growing stock volume

Species Billion Billion Wetwood Study board feet Percent cubic feet Percent Class.? priorityZ/

Western softwoods: Douglas-f ir 520.640 27.3 96.861 22.4 1 Western hemlock 251.012 13.2 47.540 11 .o 3 1 True fir 218.772 11.5 45.326 10.5 2-3 2 Ponderosa and Jeffrey pine 189.897 10 .o 38.292 8.9 1-2 Spruce (Sitka, Engelmann, etc.) 132.225 6.9 26.296 6.1 1 Lodgepole pine 65.273 3.4 25.530 5.9 1 Su gar p ine 23.520 1.2 4.344 i.0 2 4 Western white pine 20.872 1.1 3.993 .9 2 4 Western redcedar 40.897 2.2 8.106 1.9 2 Western larch 31.256 1.6 6.753 1.6 2 Redwood 23.627 1.2 4.428 1.0 2 Other western species 31.362 1.7 6.886 1.6 1 Total 1,549.353 81.3 314.355 72.8

Eastern softwoods: Shortleaf and lobloily pine 196.502 10.3 53.571 12.4 1 Longleaf and slash pine 44.248 2.3 13.855 3.2 1 White and red pine 26.874 1.4 8.349 1.9 1-2 Spruce and balsam fir 23.485 1.2 17.322 4.0 1-3 Cypress 19.112 1.o 5.033 1.2 1 Eastern hemlock 16.178 .9 5.781 1.3 3 Other eastern species 29.534 1.6 13A11 3.2 1 Total 355.933 18.7 117.522 27.2 Total softwoods 1,905.286 100 431.877 100

Eastern hardwoods: Red oak 106.217 20.6 39.309 18.1 2 3 White oak 78.689 15.3 32.099 14.8 1-2 3 Hickory 30.914 6.0 12.583 5.8 1-2 Soft maple 23.871 4.6 15.070 6.9 2 Hard maple 25.757 5.0 11.731 5.4 1 Sweet gum 26.318 5.1 10.528 4.8 2 Tupelo and black gum 25.506 5.0 9.817 4.5 2 Yellow poplar 25.093 4.9 8.570 4 .O 2 Cottonwood and aspen 16.771 3.3 12.096 5.6 2-3 Ash 15.957 3.1 7.736 3.6 2 Beech 15.649 3 .O 5.794 2.7 2 Black cherry 6.904 1.3 3.488 1.6 1 Basswood 8.502 1.6 3.434 1.6 1 Yellow birch 7.324 1.4 3.249 1.5 2 Other eastern species 46.313 9.0 22.178 10.2 1-2 To ta1 459.785 89.2 197.682 91.1

Western hardwoods: Red alder 24.842 4.8 7.638 3.5 1-2 Cottonwood and aspen 12.077 2.3 5.043 2.3 2-3 Oak 3.064 .6 1.606 .8 2 Other western species 15.713 3.1 5.043 2.3 1-2 Total 55.696 10.8 19.330 8.9 Total hardwoods 515.481 100 217.012 100

L/Class 1 species are least affected with wetwood; class 3 are most susceptible. 211 = highest; blanks indicate species with a priority lower than 4.

36 Table 9--Values of sawtimber stumpage and typical kiln-dried lumber prices for tree species with high priority for incorporation in a research program on wetwood

value of Kiln-dried lumber Study sawtimber Species priorit yl/ s t um page? Grade Thickness 1978 price?/ Dollars per thousand Dollars Inches board feet Western softwoods : Western hemlock 46,245,409 Finish FG, C and Better selects 4/4 569 Mountain hemlock 344,395 No. 2 and Better, Hem-fir Dimension 8/4 244 Total 46,589,804 White, grand, and miscellaneous firs 24,234,647 NoDle fir 5,046 ,826 Moulding and Better, rough dry 5/4, 6/4 526-562 Shasta red fir 2 ,097,222 No. 2 and Better Dimension 8/4 236 Subalpine fir 601,378 Total 31,980,073 Sugar and western white pine 40,004,600 C and Better Selects, S2S 4/4, 5/4, 6/4, 8/4 944-1,010 Moulding, S2S 4/4, 5/4, 6/4, 8/4 463-761 Eastern hardwood: Oak 1,328,917 No. 1 Common and Better 4/4, 5/4 800-1 ,100

L/1 = highest. /Value of sawtimber stumpage sold from National Forests in 1976 (143). /Averaged prices for softwood (Western Wood Products Association,-rtland, Oreg. ) and range of prices for oak (Hardwood Market Report, Volume 56, Memphis, Tenn. ) .

High priority should be given to three items of concern in the area of research to develop improved processing methods for timber and wood products containing wetwood:

1. Develop an accurate and fast method for identifying wetwood in green lumber and Material for the corollary studies on veneer to segregate the pieces into drying wetwood properties and processing should be sorts. selected from sample trees, logs, and wood products of the product and yield studies. 2. Determine optimum methods for processing Studies of wetwood properties should be sorts of lumber and veneer containing pure designed to aid development of practical and and mixed amounts of wetwood and normal wood. accurate methods for detecting wetwood in timber and solid wood products in the green 3. Compare mechanical strength properties of condition. Studies on processing methods lumber containing wetwood with similar should determine, both qualitatively and lumber of normal wood content for light quantitatively, the wood losses, grade frame construction. changes, and energy requirements for producing end products containing wetwood so There are good possibilities to design that comparisons could be made with products studies which could examine all three items. containing normal wood. Results and feedback from the corollary studies would increase the efficiency and accuracy of timber quality evaluation and prediction of product.potentia1 for the commercial wood processor.

37 Investigations to determine optimum methods The influence of wetwood on strength of drying boards and veneers containing properties of lumber for light frame wetwood should probably be conducted in construction is not known. We can safely tandem with investigations to characterize assume, though, that wetwood probably has a and sort these products before they are detrimental efiect because of the frequent dried. It would be useful to design these occurrence of deep surface checks, processing studies so that any development honeycomb, and shake in the dried lumber of drying defects could be related back to that reduces the resistance to shear. micro-organisms in the tree. The spread of Shake is closely limited in stress-graded bacteria from wetwood zones to sapwood lumber for construction, particularly in during log storage needs to be investigated members subject to bending (194). The data with respect to formation of chemical brown in table 7 suggest that wetwood may cause stain and changes in permeability of the particleboard intended for structural sapwood. Definitive biochemical studies of purposes to have lower strength values than contributing micro-organisms can also be boards made entirely from normal wood. The considered a long-term research need. importance of investigating the influence of wetwood in structural lumber and other A particular short-term research need must building components cannot be be the processing of boards and veneer overemphasized. According to Suddarth containing mixtures of wetwood and normal (184) I the light-frame building is the wood. As was pointed out for white fir predominant form of construction (147)and western hemlock (110), boards worluwide. Consequently, technological containing wood of a mixed drying sort gains in light-frame construction can present additional problems for drying and vitally affect large segments of the planing which have been ignored. Green world's population. boards and veneer containing mostly wetwood, if properly presorted, can be dried under Long-Ter m special schedules. No data are presently available, however, for delineating The objectives of a long-term research characteristics of mixed wood sorts that program should be mainly concerned with would properly identify and permit attacking the causes of wetwood. Additional presorting these products for drying. basic research aimed at reducing energy and Techniques for drying mixed wood boards and wood losses during the processing of wetwood veneer for optimum yields and energy con- may also be needed. Specific plans for sumption must be considered a short-term long-term research will depend somewhat on need of high priority. the initial information derived from short-term research, together with recommendations from workers in the fields of forest biology and timber management.

38 Knowledge of specific patterns and location It is important to explore the possibility of wetwood in standing trees gained largely that bacteria in wetwood may enhance its from short-term research will provide the subsequent decay by fungi if anaerobic basis for planning long-term investigations conditions are lost, such as by frost of the causes of wetwood. The role of cracks. Hartley et al. (2)noted that micro-organ i sms, e spec ially anaerobic fungal wood decay can be accelerated by the bacteria, need to be investigated. To be presence of bacteria but did not consider meaningful, though, research on microbiology the possibility that wetwood bacteria may must be coordinated with investigations of provide a source of nitrogen and vitamins other possible causes. There is a need to for fungal growth. Nitrogen-fixing bacteria investigate possible contributions by the have been considered in more recent following agents: insects, fungi, mistletoe, paper*/ (3, 4, 22). Nitrogen fixation oxygen and water stress, fire, and by bacteria has even been associated with mechanical wounds associated with timber sporophores of decay fungi on western management and recreational uses of the hemlock trees (118). In addition, Bourchier forest. (3)found that bacteria from wetwood can produce vitamins which enhance the growth of Identification and biochemical character- wood-decaying fungi. ization of the bacterial populations associated with wetwood can help to solve Studies of bacterial populations in wetwood current wood processing problems and provide must also be concerned with distinguishing a basis for future control of wetwood inocuous plant and.soi1 bacteria from formation in trees. The biochemical pathogenic and fecal coliforms by serology, contribution of pectolytic and cell wall analysis, and deoxyribonucleic phenyloxidizing bacteria to shake and frost acid homology studies.30/ The presence of cracks in trees and to surface checking, coliform bacteria in living wood tissues honeycomb, collapse, ring failure, and (13)can be a problem in some uses of wood chemical brown stain in wood products needs products, such as redwood for water storage to be more thoroughly defined and related to tanks (166). the initial formation of wetwood.

z/S. D. Spano, M. F. Jurgensen, M. J. Larsen, and A. E. Harvey. 1978. Nitrogen fixation in decaying Douglas fir residue. Paper presented at 70th Annual Meeting of the American Society of Agronomy, 11 p. Madison, Wis. X/J. G. Zeikus, University of Wisconsin, Department of Bacteriology, Madison, personal communication to J. C. Ward.

39 Once the causes of wetwood are understood, With current economic conditions, the goal there are two methods for control: direct of timber managers must be to grow and indirect. Long-term research should sawtimber that will not develop wetwood evaluate the relative merits of each before financial maturity. Indirect or method. In the practice of forestry, direct preventive control measures necessary to control of tree diseases and insect injuries achieve this goal can be obtained from is generally not as practical or economical forest biology and tree genetics research. as indirect measures of control. Direct This research must correlate the mechanisms methods, such as chemical spraying, are more of genetic resistance to wetwood formation practical with agricultural crops than with with the influences of site and cultural long-term timber crops which have a lower practices. Benefits from a long-term value per unit of ground. Still, direct research program could include: measures of control have been successfully used in forest management and must be 1. Determination or development of trees considered for preventing wetwood. Tree that are genetically resistant to formation species susceptible to wetwood during early of wetwood. stages of growth may require aerial spraying and soil fumigation. Special thinning 2. Determination of growing conditions methods and fertilization may also be needed that will prevent or minimize formation of in these young-growth stands, but wetwood is wetwood in susceptible tree species before sometimes reported to be more prevalent in the trees reach financial maturity for dominant, fast-growing trees than in sawtimber. suppressed or slow-growing trees (45, 2, 181). 3. Development of cultural and harvesting practices that will minimize the tendency for wetwood to form in residual trees or in The rotation age for sawtimber could be regeneration. reduced for species that develop wetwood with advancing age. When guidelines are developed for this type of control, it is also necessary to determine the influence of site factors and genetic makeup of the tree species on its resistance or susceptibility to wetwood with aging. If wetwood develops in young trees before sawtimber size is reached, direct control measures could be aided by research on the utilization and processing of the timber. Pole-size or presawtimber stands might be converted into products of higher unit value than the present end uses for pulp and paper. The development of more efficient drying and machining methods could even allow young trees with wetwood to profitably grow to sawtimber size.

40 Conclusion Literature Cited

From this overview, it is apparent that wetwood is responsible for substantial losses of wood, energy, and production expenditures in the forest products industry. These losses result from a raw material anomaly that in the past has either not been recognized or has been ignored. Though there is a definite need to assess more thoroughly these losses and to find ways of eliminating or minimizing them, there is also a need to examine the cause; i.e., wetwood. The fact that more and more problems in utilization and 1. Abe, Z., and K. Minami. processing of timber are recognized as 1976. [Ill smell from the wood of related directly or indirectly to wetwood Gonystylus Bancanus (Miq.) Kurz. I. clearly demonstrates the importance of this Source of ill smell. 11. Smelling phenomenon. components.] J. Jap. Wood Res. SOC. (Mokuzai Gakkaishi) 22 (2) :119-122. An effective program of research is needed [ In Jap .] to determine the significance of wetwood in these problems. This program should plan 2. Aho, P. E. and provide for obtaining both short- and 1977. Decay of grand fir in the long-term solutions to the overall Blue Mountains of Oregon and problem. Because of increasing interest in Washington. USDA For. Serv. Res. wetwood, excellent opportunities now exist Pap. PNW-229, 18 p. Pac. Northwest to initiate such a comprehensive research For. and Range Exp. Stn., Portland, program. Oreg .

There can be little doubt that the effects 3. Aho, P. E., and A. Hutchins. of wetwood on the forest products industry 1977. Micro-organisms from the pith are real, and the impact is far reaching. region of suppressed grand fir With dwindling timber supplies, increasing understory trees. USDA For. Serv. costs of available energy, and a scarcity Res. Note PNW-299, 5 p. Pac. of low cost capital, the timber industry Northwest For. and Range Exp. Stn., can no longer afford to ignore the problems Portland, Oreg. associated with wetwood, for wetwood has an impact on all these issues. 4. Aho, P. E., R. J. Seidler, H. J. Evans, and P. N. Raju. It is time we examine, in depth, the 1974 . Dis tri but ion, enumeration, detrimental effects of wetwood during all and identification of nitrogen- phases of timber production--from the stump fixing bacteria associated with to the finished product. Losses related to decay in living white fir trees. wetwood, which in the past were accepted as Phytopathology 64 (11):1413-1420. part of the package of doing business or thought to be the result of inadequate 5. Anderson, A. B., E. L. Ellwood, E. processing, can no longer be viewed in that Zavarin, and R. W. Erickson. context. A fuller understanding of the 1960. Influence of extractives on characteristics of wetwood, whether in the seasoning stain of redwood lumber. tree, log, or product, will provide timber For . Prod. J. 10(4) :212-218. managers and processors with the tools to handle the wetwood problem.

41 6. Anderson, A. B., and W. B. Fearing. 13. Bagley, S. T., R. J. Seidler, H. W. 1961. Distribution of extractives Talbot, Jr., and J. E. Morrow. in solvent seasoned redwood lumber. 1978. Isolation of Klebsielleae For. Prod. J. ll(5):240-242. from within living wood. Appl. and Environ. Microbiol. 36 (1):178-185. 7. Arganbright, D. G., and W. A. Dost. 1972. The effect of brown stain on 14. Baker, G. drying characteristics of sugar 1951. The effect of log storage pine - preliminary observations. time on development of brown stain Proc. 23d Annu. Meet. West. Dry Kiln in northern white pine (during kiln Clubs, p. 46-53. Oreg. State Univ., seasoning). Univ. Maine For. Dep. Cor va 11 i s . Tech. Note No. 8, 1 p. Orono.

8. Arganbright, D. G., and R. Smith. 15. Barton, G. M. 1978. General drying 1968. Significance of western characteri s t ics of young-g rowth hemlock phenolic extractives in redwood. Tech. Rep. 35.01.156, 25 p. pulping and lumber. For. Prod. J. Univ. Calif. For. Prod. Lab., 18 (5) :76 -80. Richmond. 16. Barton, G. M. 9. Arganbright, D. G., and W. W. Wilcox. 1972. How to prevent dry kiln 1969. Comparison of parameters for corrosion. Can. For. Ind. predicting permeability of white 92 (4): 27 -29. fir. Proc. Am. Wood-Preserv. Assoc. 65: 57-62. 17. Barton, G. M. 1973. The significance of western 10. Arni, P. C., G. C. Cochrane, and J. D. hemlock phenolic extractives in Gray. groundwood pulping . Tappi 1965. The emission of corrosive 56(5) :115-118. vapours by wood. I. Survey of acid-release properties of certain 18 . Barton, G. M., and J. A. F. Gardner. freshly felled hardwoods and 1966. Brown stain formation and the softwoods. J. Appl. Chem. phenolic extractives of western 15(July) :305 -313. hemlock (Tsuga heterophylla (Raf.) Sarg.) Dep. For. Publ. 1147, 20 p. 11. Arni, P. C., G. C. Cochrane, and J. D. Ottawa, Can. Gray. 1965. The emission of corrosive 19. Barton, G. M., and R. S Smith. vapours by wood. 11. The analysis 1971. Brown stain in kiln-dried of vapours emitted by certain Abies amabilis lumber. Bi-Mon. Res. freshly felled hardwoods and Notes 27(3) :21-23. Dep. Fish. and softwood by gas chromatography and For., Ottawa, Can. spectrophotography. J. Appl. Chem. 15(&t.) :463-468. 20. Bauch J., W. Hgll, and R. Endeward. 1975. Some aspects of wetwood 12. Bacon, M., and C. E. Mead. formation in fir. Holzforschung 1971. Bacteria in the wood of 29(6) :198-205. living aspen, pine, and alder. Northwest Sci. 45(4) :270-275.

42 21. Bauch, J., W. Liese, and H. Berndt. 29. Bramhall, G., and R. W. Wellwood. 1970. Biological investigations for 1976. Kiln drying of western improvement of permeability of Canadian lumber. Inf. Rep.VP-X-159, softwoods.% Holzforschung 112 p. Dep. Fish. and the 24 (6) :199-205. Environment, Can. For. Serv. West. For. Prod. Lab., Vancouver, B.C. 22. Blanchette, R. A., and C. G. Shaw. 1978. Associations among bacteria, 30. Bryan, E. L. yeasts, and basidiomycetes during 1960. Collapse and its removal in wood decay. Phytopathology Pacific madrone. For. Prod. J. 68 (4) :631-637. lO(11) :598-604.

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42. Cole, E. J., Jr., and F. A. Streams. 47. Day, W. R. 1970. Insects emerging from brown 1929. The watermark disease of the slime fluxes in southern New cricket-bat willow (Salhx England. Can. Entomol. caerulea). Oxford For. Mem. 3, 30 102(3) :321 -333 . p. Oxford Univ. Press, Oxford, England . 43. Comstock, G. L. 1975. Energy requirements for 48. Dokken, M., and R. Lefebvre. drying of wood products. Wood 1973. Drying veneer peeled from residues as an energy source. Proc. seven New Brunswick balsam fir P-75-13, p. 8-12. For. Prod. Res. logs. Can. Dep. Environ. Info Rep. SOC., Madison, Wis. OP-X-60, 20 p. Ottawa.

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100. Knauss, A. C., and E. H. Clarke. 107. Knutson, D. M. 1961. Seasoning and surfacing 1973. The bacteria in sapwood, degrade in kiln-drying western wetwood and heartwood of trembling hemlock in western Oregon. USDA aspen. Can. J. Bot. 51(2) :498 -500. For. Serv. Pac. Northwest For. and 8 Range Exp. Stn. Res. Note 207, 108. Kollmann, F. F. P. , and W. A. Cote, Jr. 11 p. Portland, Oreg. 1968. Principles of wood science and technology. I. Solid wood. 101. Knight, E. 592 p. Springer-Verlag, New York. 1955. Identification of white fir drying sorts. Western Pine Assoc. Res. Note 4.213, 5 p. 109. Kozlik, C. J. 1971. Electrical moisture meter Portland, Oreg. readings on western hemlock dimension lumber. For. Prod. J. 102. Knight, E. 21(6) :34-35. 1959. The elimination of sugar pine brown stain. Proc. 11th Annu. 110. Kozlik, C. J., and L. W. Hamlin. Meet. West. Dry Kiln Clubs, p. 25-30. Oreg. State Univ., 1972. Reducing variability in final moisture content of kiln Corvallis. dried western hemlock lumber. For. Prod. J. 22(7) :24-31. 103. Knight, E. 1970. Kiln drying western 111. Kozlik, C. J., R. L. Krahmer, and R. softwoods. Bull. 7004, 77 p. T. Lin. Moore Dry Kiln Coo Oreg., 1972. Drying and other related Portland, Oreg. properties of western hemlock sinker heartwood. Wood and Fiber 4(2) :99-111.

48 112. Krahmer, R. L., R. W. Hemingway, and W. E. Hillis. 1970. The cellular distribution of lignans in Tsuqa heterophylla wood. Wood Sci. and Technol. 4 (2) :122-139.

113. Kubler, H. 1959. [Studies on growth stresses in trees.] Part I. The origin of growth stresses and stresses in transverse direction. 3 Holz Roh Werkst. 17(1) :1-9. [In Ger.] 120. Lin, R. T., and C. J. Kozlik. 1971. Permeability and drying 114. Kubler, H. behavior of western hemlock. Proc. 1959. [Studies on growth stresses 22d Annu. Meet. West. Dry Kiln in trees. Part 11. Longitudinal Clubs, p. 44-50. Oreg. State stresses.] Holz Roh Werkst. Univ., Corvallis. 17(2):44-54. [In Ger.] 121. Lin, R. TotE. P. Lancaster, and R. 115. Kubler, H. L. Krahmer. 1959. [Studies on growth stresses 1973. Longitudinal water in trees. Part 111. Effect of permeability of western hemlock. heat treatment on the dimensions of I. Steady-state permeability. green wood.] Holz Roh Werkst. Wood and Fiber 4(4) :278-289. 17(3) :77-86. [In Ger.] 122. Linzon, S. N. 116. Kutsche, N. P., and R. L. Ethington. 1958. Water content variation in 1962. Shelling failures. For. the heartwood of white pine and its Prod. J. 12(11):538. relation to incipient decay. For. Chron. 34(1) :48-49. 117. Lagerberg, T. 1935. Barrtgrgdens Vattved. 123. Linzon, S. N. [Wetwood in conifers.] Sven. 1962. Artificial inoculation of Skogsvardsforeningens Tidskr . wet and dry heartwood of living 33 (3) :177-264. eastern white pine trees.. For. Sci. 8(2) :163-167. 118 . Larsen, M. J., M. F. Jurgensen, A. E. Harvey, and J. C. Ward. 124. Lockard, C. R., J. A. Putnam, and R. 1978. Dinitrogen fixation D. Carpenter. associated with sporophores of 1963. Grade defects in hardwood Fomitopsis pinicola, Fomes timber and logs. U.S. Dep. Agric. fomentarius, and Echinodontium Agric. Handb. 244, 39 p. tinctorum. Mycologia 70 (6) :1217 -1222. 125. Lutz, J. F. 1971. Wood and log characteristics 119. Liese, W., and G. Karnop. affecting veneer production. USDA 1968. [On the attack of coniferous For. Serv. Res. Pap. FPL-150, 31 p. wood by bacteria.] Holz Roh For. Prod. Lab., Madison, Wis. Werkst. 26(6) :202-208. [In Ger.1

49 126. Lutz, J. F. 135. MacLean, H., and J. A. F. Gardner. 1972. Veneer species that grow in 1951. Deterioration of wooden dry the United States. USDA For. Serv. kilns used for drying western Res. Pap. FPL-167, 129 p. For. hemlock lumber. Lumberman Prod. Lab., Madison, Wis. 78 (12) :88 -90.

127. McGinnes, E. A., Jr. 136. MacLean, H., and J. A. F. Gardner. 1965. Extent of shake in Missouri 1956. Distribution of fungicidal oaks. For. Prod. J. 15(5):190. extractives (Thujaplicin and water-soluble phenols) in western 128. McGinnes, E. A., Jr. redcedar heartwood. For. Prod. J. 1968. Extent of shake in black 6 (12) :510 -516. walnut. For. Prod. J. 18(5):80-82. 137. McMillen, J. M. 129. McGinnes, E. A., Jr., C. I. J. Chang, 1953. Kiln drying water and swamp and K. Y. T. Wu. tupelo. J. For. Prod. Res. SOC. 1971. Ring shake in some hardwood 3(5) :iag-i96. species. Individual tree approach. J. Polym. Sci., Part C., 138. Manson, B. C. No. 36, p. 153-176. Interscience 1949. The drying of California Publ., New York. redwood. Calif. Redwood Assoc. Res. Rep. 1, 8 p. San Francisco. 130. McGinnes, E. A. , Jr. , J. E. Phelps, and J. C. Ward. 139. Meyer, R. W., and G. M. Barton. 1974. Ultrastructure observations 1971. A relationship between of tangential shake formations in collapse and extractives in western hardwoods. Wood Sci. 6(3) :206-211. redcedar For . Prod. J. 21 (4) :58 -60.

131. McIntosh, J. A., and T. Szabo. 140. Meyer, R. W., and L. Leney. 1972. Watch for these signs of 1968. Shake in coniferous wood: white spruce heartshake. Can. For. An anatomical study. For. Prod. J. Ind. 92(10) :68-69, 71. 18 (2) :51 -56.

132. MacKay, J. F. G. 141. Millett, M. M. 1974. High-temperature kiln-drying 1952. Chemical brown stain in of northern aspen 2- by 4-inch sugar pine. J. For. Prod. Res. light-framing lumber. For. Prod. SOC. 2(5) :232-236. J. 24 (10) :32-35. 142. Panshin, A. J., and C. de Zeeuw. 133. MacKay, J. F. G. 1970. Text book of wood 1975. Properties of northern aspen technology. Vo1. I. 3d ed. 705 p. discolored wood related to drying McGraw-Hill Book Co., New York. problems. Wood and Fiber 6 (4) :319 -326. 143. Phelps, R. B. 1977. The demand and price 134. MacKay, J. F. G. situation for forest products, 1976. Delayed shrinkage after 1976-77. U.S. Dep. Agric. Misc. surfacing of high-temperature Publ. 1357, 95 p. kiln-dried northern aspen dimension lumber. For. Prod. J. 26(2) :33-36.

50 144. Poluboyarinov, 0. I. 152. Resch, H., E. T. Choong, and H. H. 1963. [The nature and some Smith. properties of aspen.] Nauchn. Tr. 1968. Sorting incense cedar types Leningr. Lesotekh. Akad. for drying. For. Prod. J. 102:37-44. [In Russ.] 18 (4) :40 -44.

145. Pong, W. Y. 153. Resch, H., and B. A. Ecklund. 1971. Changes in grade and volume 1964. Accelerating the drying of of central California white fir redwood lumber. Calif. Agric. Exp. lumber during drying and Stn. Bull.. 803, 27 p. Univ. surfacing. USDA For. Serv. Res. Calif. Div. Agric. Sci., Berkeley. Note PNW-156, 20 p. Pac. Northwest For. and Range Exp. Stn., Portland, 154. Resch, H., B. A. Ecklund, and D. R. Oreg . Pre s t emo n . 1963. Tanoak drying program and 146. Pong, W. Y., and G. H. Jackson. shrinkage characteristics. Calif. 1971. Diagraming surface Agric. (Oct,), p. 12-14. Univ. characteristics of true fir logs. Calif. Div. Agric. Sci. , Berkeley. Supplement to log diagraming guide for western softwoods. USDA For. 155. Rietz, R. C., and R. H. Page. Serv. Pac. Northwest For. and Range 1971. Air drying of lumber: A Exp. Stn., 7 p., Portland, Oreg. guide to industry practices. U.S. Dep. Agric. Agric. Handb. 402, 147. Pong, W. Y., and W. W. Wilcox. 110 p. 1974. Spatial distribution of lumber degrade in white fir trees. 156. Rosen, H. N. USDA For. Serv. Res. Pap. PNW-184,' 1978. High temperature predrying 18 p. Pac. Northwest For. and of wood. Proc. 29th Annu. Meet. Range Exp. Stn., Portland, Ores. West. Dry Kiln Clubs, p. 1-10. Oreg . State Univ. , Corvallis. 148. Pratt, M. B. 1915. The deterioration of 157. Rossell, S. E., E. G. M. Abbot, and lumber. Calif. Agric. Exp. Stn. J. F. Levy. Bull. 252, p. 301-320, Berkeley. 1973. A review of the literature relating to the presence, action, 149. Random Lengths. and the interaction of bacteria in 1976. Yearbook. Vo1. 12. 118 p. wood. J. Inst. Wood Sci.' David S. Evans, ed. Random Lengths 6(2) :28-35. Publ., Inc., Eugene, Oreg. 158. Sachs, I. B., J. C. Ward, and R. E. 150. Random Lengths. Kinney. 1977. Yearbook. Vo1. 13. 186 p. 1974. Scanning electron microscopy David S. Evans, ed. Random Lengths of bacterial wetwood, sapwood, and Publ., Inc., Eugene, Oreg. normal heartwood in poplar trees. Proc. 7th Annu. Scanning Electron 151. Rasmussen, E. F. Microsc. Symp., Part 2, 1961. Dry kiln operators manual. p. 453-460. ZIT Res. Inst., U.S. Dep. Agric. Agric. Handb. 188, Chicago. 197 p.

51 159. Salamon, M. 1961. Kiln drying of British Columbia softwoods at high temperatures. Proc. 13th Annu. Meet. West. Coast Dry Kiln Clubs, p. 29-35. Oreg. State Univ., Corvallis.

160. Salamon, M. 1973. Drying of lodgepole pine and spruce studs cut from flooded timber: A progress report. Proc. 24th Annu. Meet. West. Dry Kiln Clubs, p. 51-56. Oreg. State 167. Seliskar, C. E. Univ., Corvallis. 1950. Some investigations on the wetwood diseases of American elm 161. Salamon, M., and K. Urquhart. and Lombardy poplar. Ph.D. 1972. 55-hour kiln schedule for thesis. Cornel1 Univ., Ithaca, N.Y. l$-in. dry spruce. Can. For. 137 p. Ind. 92(5):67, 69. 168. Seliskar, C. E. 162. Schafer, R. F. 1952. Wetwood organism in aspen, 1974. How to kiln-dry mixed stock poplar is isolated. Colo. Farm and for uniform moisture content. Can. Home Res. 2(6):6-11, 19-20. Colo. For. Ind. 94(3) :67-68. State Univ. Fort Collins.

163. Schirp, M. 169. Sherrard, E. C., and E. F. Kurth. I1 of 1968. Frostrisse an baumstammen. 1933. The distribution Forstarchiv 39(7):149-154. extractives in redwood: Its relation to durability. Ind. Eng. Chem. 25 (3): 300-302. 164. Schrenk, H. von. 1905. Glassy fir. Rep. Mo. Bot, Gard. Annu. 16, p. 117-120. St. 170. Shields, J. K., R. L. Desai, and M. Louis, Mo. R. Clarke. 1973. Control of brown stain in kiln-dried eastern white pine. 165. Schroeder, H. A., and C. J. Kozlik. 1972. The characterization of For. Prod. J. 23(10) :28-30. wetwood in western hemlock. Wood Sci. and Technol. 6(2) :85-94. 171. Shigo, A. L. 1967. Successions of organisms in 166. Seidler, R. J., J. E. Morrow, and S. discoloration and decay of wood. T. Bagley. Int. Rev. For. Res. 2:237-29-9. 1977. Klebsielleae in drinking water emanating from redwood 172. Shigo, A. L. tanks. Appl. and Environ. 1972. Ring and ray shakes Microbiol. 33(4) :893-900. associated with wounds in trees. Holzforschung 26 (2) :60 -62.

52 173. Shigo, A. L.,, and W. E. Hillis. 181. Stojano.v, V., and E. Enthev. 1973. Heartwood, discolored wood, 1968. [Properties of silver fir and microorganisms in living wetwood.] Gorskostop Nauka Sofija trees. Annu. Rev. Phytopathol. 5(5) :61-73. [In Bulgarian.] 11 :19 7 -22 2 . 182. Stutz, R. E. 174. Shigo, A. L., J. Stankewich, and B. 1959. Control of brown stain in J. Cosenga. sugar pine with sodium azide. For. 1971. Clostridium z.associated Prod. J. 9(12) :459-463. with discolored tissue in living oaks. Phytopathology 61(1) :122-123. 183. Stutz, R. E., and A. W. Stout. 1957. The nature of brown stains 175. Simpson, W. T. in timber from the western pines. 1975. Effect of steaming on the Proc. Plant Physiol. Meet. Plant drying rate of several species of Physiol. V 32, Suppl. 13, (Aug. wood. Wood Sci. 7(3) :247-255. 25). Am. SOC. Plant Physiol., Bethesda, Md. 176. Smith, H. H. 1956. Improved utilization of 184. Suddarth, S. K. western hardwoods by modern 1973. Research needs in drying. For. Prod. J. 6(3) :121-124. light-frame construction. Res. Bull. 903, 57 p. Wood Res. Lab., Purdue Univ., Lafayette, Ind. 177. Smith, H. Hot and J. R. Dittman. 1960. Drying rate of white fir by segregations. USDA For. Serv. 185. Svidenko, A. I. Pac. Southwest For. and Range Exp. 1970. [Damage to Juqlans reqia.by Stn. Res. Note 168, 10 p. frost cracks in the Bukovina region Berkeley, Calif . (Ukraine) .I Lesoved. , Mosk. 1970.(l):89-90. [In Russ.] 178. Smith, H. H., and J. R. Dittman. 1960. Moisture content in 186 . Takizawa, To, N. Kawaguchi, M. kiln-dried lumber. For. Prod. J. Takahashi, and H. Yamamoto. 10 (7) :353-357. 1976. [The observation of the wetwood of Todomatsu (Abies 179. Smith, H. H., and J. R. Dittman. sachalinesis Mast.)] J. Hokkaido 1960. The segregation of white fir For. Prod. Res. Inst. 294(July) :6-11., [In Jap.] for kiln drying. USDA For. Serv. Pac. Southwest For. & Range Exp. Stn. Res. Note 167, 6 p. Berkeley, 187. Terashima, N. Calif . 19.75. Odor problems. Mokuzai Kog. 30(11) :32-34. Wood Tech. Assoc. Jap., Tokyo 105. [In Jap.] 180. Smith, R. S. 1975. Economic aspects of bacteria in wood. 2 Proceedings of sessions on wood product's pathology and 2nd International Congress of Plant Pathology, Sept . 10-12, 1973, Minneapolis, Minn. Spr inger-Ver lag, New Yor k .

5.3 188. Thomas, D. P., and H. D. Erickson. 1963. Collapse and honeycomb in western red cedar in relation to green-wood liquid permeability. Proc. 15th Annu. Meet. West. Coast Dry Kiln Clubs, p. 7-14. Oreg. State Univ., Corvallis.

189. Thunell, B. 1947. On the technical properties of wetwood. For. Abstr. 8 (3) :400 -401.

190. Tiedemann, G., J. Bauch, and E. Bock. 1977. Occurrence and significance of bacteria in living trees of Populus nigra L. Eur. J. For. 196. Wagener, W. W. Pathol. 7 (6) :364-374. 1970. Frost cracks A common defect in white fir in California. 191. Toole, E. R. USDA For. Serv. Res. Note PSW-209, 1968. Wetwood in cottonwood. 5 p. Pac. Southwest Foro and Range Plant Dis. Rep. 52(10) :822-823. Exp. Stn., Berkeley, Calif. 192. U.S. Department of Agriculture, 197. Wallin, W. B. Forest Service. 1954. Wetwood in balsam poplar. 1973. The outlook for timber in Minn. For. Notes 28, Agric. Exp. the United States. USDA For. Serv. Stn. Sci. J. Ser. Pap. 3118, 2 p. For. Resour. Rep. FRR-20, 367 p., Univ. Minn. , St. Paul. illus. U.S. Gov. Print. Off., Washington, D.C. 198. Wangaard, F. F. 1978. Anatomy and behavior of 193. U.S. Department of Agriculture, early wood in relation to water Forest Service. stress in living trees. Abstr., 1977. The Nation's renewable 32d Annu. Meet. For. Prod. Res. resources: An assessment, 1975. SOC., p. 33. Madison, Wis. USDA For. Serv. For. Resour. Rep. FRR-21, 243 p. U.S. Gov. Print. 199. Ward, J. C. Off., Washington, D.C. 1972. Anaerobic bacteria associated with honeycomb and ring 194. U.S. Forest Products Laboratory. failure in red and black oak 1974. Wood handbook: Wood as an engineering material. U.S. Dep. lumber . (Abstr . ) Phytopathology Agric. Agric. Handb. 72. 62 (7) :796.

195. Unligil, H. H. 1969. Penetrability of white spruce wood after water storage. J. Inst. Wood Sci. 5(6) :30-35.

54 200 . Ward, J. C. 206. Ward, J. C., and E. M. Wengert. 1976. Kiln drying characteristics 1974. Bacterial wetwood: How it of studs from Rocky Mountain aspen affected wood drying quality in and Wisconsin aspen. 3 aspen. Proc. 3d North Am. For. Utilization and marketing as tools Biol. Workshop, p. 382. Colo. for aspen management in the Rocky State Univ., Fort Collins. Mountains. USDA For. Serv. Gen. Tech. Rep. RM-29, p. 73-74. Rocky 207. Ward, J. C., M. F. Wesolowski, and A. Mt. For. and Range Exp. Stn., Fort L. Shigo. Collins, Colo. 1978. The use of electrical resistance for detecting 201. Ward, J. C. hard-to-dry lumber containing 1978. Honeycomb: Dry kiln or bacterial wetwood. Abstr., 32d bacteria. Abstr., 32d Annu. Meet. Annu. Meet. For. Prod. Res. SOC., For. Prod. Res. Soc., p. 30. p. 36. Madison, Wis. Madison, Wis. 208. Ward, 0. Po,, and W. M. Fogarty. 202. Ward, J. Cot R. A. Hann, R. C. 1973. Bacterial growth and enzyme Baltes, and E. H. Bulgrin. production in Sitka spruce (Picea 1972. Honeycomb and ring failure sitchensis) sapwood during water in bacterially infected red oak storage. J. Inst. Wood Sci. lumber after kiln drying. USDA 6 (2) :8 -12. For. Serv. Res. Pap. FPL-165, 36 per illus. For. Prod. Lab., 209. Warren-Wren, S. C. Madison, Wis. 1965. The significance of the caerulean or cricket-bat willow 203. Ward, J. C., and C. J. Kozlik. (Salix- -alba L. cultivar "calva") . 1975. Kiln drying sinker heartwood Q. J. For. S9(3) :193-205. from young-growth western hemlock: Preliminary evaluation. Proc. 26th 210. Western Wood Products Association. Annu. Meet. West. Dry Kiln Clubs, 1977. Grading rules for western p. 44-63. Oreg. State Univ., lumber. 4th ed. 202 p., illus. Corva 11 i s . Portland, Oreg .

204. Ward, J. C., J. E. Kuntz, and E. 211. Wickman, B. E., and R. F. Scharpf. McCoy . 1972. Decay in white fir 1969. Bacteria associated with top-killed by Douglas-f ir tussock "shake" in broadleaf trees. moth. USDA For. Serv. Res. Pap. (Abstr.) Phytopathology 59(8) :1056. PNW-133, 9 p. Pac. Northwest For. and Range Exp. Stn., Portland, Oreg. 205. Ward, J. C., and D. Shedd 1979. California black oak drying problems and the bacterial factor. USDA For. Serv. Res. Pap. FPL-344, 14 p. For. Prod. Lab., Madison, Wis.

55 212. Wilcox, W. W. 220. Yazawa, K., S. Ishida, and H. 1968. Some physical and mechanical Miyaj ima. properties of wetwood in white 1965. On the wet-heartwood of some fir. For. Prod. J. 18(120):27-31. broad-leaved trees grown in Japan. I. J. Jap. Wood Res. SOC. 213. Wilcox, W. W. (Mokuzai Gakkaishi) ll(3):71-76. 1970. Anatomical changes in wood cell walls attacked by fungi and 221. Zeikus, J. G., and D. L. Henning. bacteria. Bot. Rev. 36(1) :1-28. 1975. Me thanobacter ium arbophilicum sp. nov. An obligate 214. Wilcox, W. W., and N. D. Oldham. anaerobe isolated from wetwood of 1972. Bacterium associated with living trees. Antonie van wetwood in white fir. Leeuwenhoek J. Microbiol. and Phytopathology 62 (3) :384 -385. Serol. 41(4) :543-552.

215. Wilcox, W. W., and W. Y. Pong. 222, Zeikus, J. G., and J. C. Ward. 1971. The effects of height, 1974. Methane formation in living radial position, and wetwood on trees: A microbial origin. white fir wood properties. Wood Science 184(4142) :1181-1183. and Fiber 3(1) :47-55. 223. Zinkel, D. F., J. C. Ward, and B. F. 216. Wilcox, W. W., W. Y. Pong, and J. R. Kukachka. Pa rmet e r . 1969. Odor problems from some 1973. Effects of mistletoe and plywoods. For. Prod. J. 19(12):60. other defects on lumber quality in white fir. Wood and Fiber 4 (4) :272-277.

217. Wilcox, W. W., and C. G. R. Schlink. 1971. Absorptivity and pit structure as related to wetwood in white fir. Wood and Fiber 2 (4) : 373-379.

218. Williston, E. M. 1971. Drying west coast dimension to meet the new lumber standards. For. Prod. J. 21(3) :44-48.

219. Wong, W. C., and T. F. Preece. 1978. Erwinia salicis in cricket bat willows: Histology and histochemistry of infected woods. Physiol. Plant Pathol. 12(3) :321 -332.

56 The Forest Service of the U.S. Department of Agriculture is dedicated to the princ,iple of multiple use management of the Nation’s forest resources for sustained yields of wood, water, forage, wildlife, and recreation. Through forestry research, cooperation with the States and private forest owners, and management of the National Forests and National Grasslands, it strives - as directed by Congress - to provide increasingly greater service to a growing Nation. The U.S. Department of Agriculture is an Equal Opportunity Employer. Applicants for all Department programs will be given equal consideration without regard to age, race, color, sex, religion, or national origin.

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